diff --git a/adapters/adform/adform_test.go b/adapters/adform/adform_test.go
index 7023ef0eb61..f677f347c0c 100644
--- a/adapters/adform/adform_test.go
+++ b/adapters/adform/adform_test.go
@@ -185,7 +185,7 @@ func preparePrebidRequest(serverUrl string, t *testing.T) *pbs.PBSRequest {
 	pbsCookie := usersync.ParsePBSCookieFromRequest(prebidHttpRequest, &config.HostCookie{})
 	pbsCookie.TrySync("adform", adformTestData.buyerUID)
 	fakeWriter := httptest.NewRecorder()
-	pbsCookie.SetCookieOnResponse(fakeWriter, "", time.Minute)
+	pbsCookie.SetCookieOnResponse(fakeWriter, &config.HostCookie{Domain: ""}, time.Minute)
 	prebidHttpRequest.Header.Add("Cookie", fakeWriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/appnexus/appnexus_test.go b/adapters/appnexus/appnexus_test.go
index cf849adaf33..2c54a37fb29 100644
--- a/adapters/appnexus/appnexus_test.go
+++ b/adapters/appnexus/appnexus_test.go
@@ -367,7 +367,7 @@ func TestAppNexusBasicResponse(t *testing.T) {
 	pc := usersync.ParsePBSCookieFromRequest(req, &config.HostCookie{})
 	pc.TrySync("adnxs", andata.buyerUID)
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	req.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/audienceNetwork/facebook_test.go b/adapters/audienceNetwork/facebook_test.go
index 78b7c868e69..304df4cdbea 100644
--- a/adapters/audienceNetwork/facebook_test.go
+++ b/adapters/audienceNetwork/facebook_test.go
@@ -209,7 +209,7 @@ func GenerateBidRequestForTestData(fbdata bidInfo, url string) (*pbs.PBSRequest,
 	pc := usersync.ParsePBSCookieFromRequest(req, &config.HostCookie{})
 	pc.TrySync("audienceNetwork", fbdata.buyerUID)
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	req.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/lifestreet/lifestreet_test.go b/adapters/lifestreet/lifestreet_test.go
index 60b6aed3656..14dda25d2a9 100644
--- a/adapters/lifestreet/lifestreet_test.go
+++ b/adapters/lifestreet/lifestreet_test.go
@@ -227,7 +227,7 @@ func TestLifestreetBasicResponse(t *testing.T) {
 
 	pc := usersync.ParsePBSCookieFromRequest(req, &config.HostCookie{})
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	req.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/pubmatic/pubmatic_test.go b/adapters/pubmatic/pubmatic_test.go
index e278e439e2b..8bf22eb0639 100644
--- a/adapters/pubmatic/pubmatic_test.go
+++ b/adapters/pubmatic/pubmatic_test.go
@@ -656,7 +656,7 @@ func TestPubmaticSampleRequest(t *testing.T) {
 	pc := usersync.ParsePBSCookieFromRequest(httpReq, &config.HostCookie{})
 	pc.TrySync("pubmatic", "12345")
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	httpReq.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/pulsepoint/pulsepoint_test.go b/adapters/pulsepoint/pulsepoint_test.go
index 71c0406a7ae..f2b86dc630d 100644
--- a/adapters/pulsepoint/pulsepoint_test.go
+++ b/adapters/pulsepoint/pulsepoint_test.go
@@ -226,7 +226,7 @@ func SampleRequest(numberOfImpressions int, t *testing.T) *pbs.PBSRequest {
 	pc := usersync.ParsePBSCookieFromRequest(httpReq, &config.HostCookie{})
 	pc.TrySync("pulsepoint", "pulsepointUser123")
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	httpReq.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 	// parse the http request
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/rubicon/rubicon_test.go b/adapters/rubicon/rubicon_test.go
index c8b7ecadbe8..a263f6bef69 100644
--- a/adapters/rubicon/rubicon_test.go
+++ b/adapters/rubicon/rubicon_test.go
@@ -945,7 +945,7 @@ func CreatePrebidRequest(server *httptest.Server, t *testing.T) (an *RubiconAdap
 	pc := usersync.ParsePBSCookieFromRequest(req, &config.HostCookie{})
 	pc.TrySync("rubicon", rubidata.buyerUID)
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	req.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 
 	cacheClient, _ := dummycache.New()
diff --git a/adapters/sovrn/sovrn_test.go b/adapters/sovrn/sovrn_test.go
index c84b0dbca7a..67d49e62ab8 100644
--- a/adapters/sovrn/sovrn_test.go
+++ b/adapters/sovrn/sovrn_test.go
@@ -188,7 +188,7 @@ func SampleSovrnRequest(numberOfImpressions int, t *testing.T) *pbs.PBSRequest {
 	pc := usersync.ParsePBSCookieFromRequest(httpReq, &config.HostCookie{})
 	pc.TrySync("sovrn", testSovrnUserId)
 	fakewriter := httptest.NewRecorder()
-	pc.SetCookieOnResponse(fakewriter, "", 90*24*time.Hour)
+	pc.SetCookieOnResponse(fakewriter, &config.HostCookie{Domain: ""}, 90*24*time.Hour)
 	httpReq.Header.Add("Cookie", fakewriter.Header().Get("Set-Cookie"))
 	// parse the http request
 	cacheClient, _ := dummycache.New()
diff --git a/config/config.go b/config/config.go
index 6eff84dac36..f60c8c86e59 100644
--- a/config/config.go
+++ b/config/config.go
@@ -59,6 +59,8 @@ type Configuration struct {
 	BlacklistedAcctMap map[string]bool
 }
 
+const MIN_COOKIE_SIZE_BYTES = 500
+
 type HTTPClient struct {
 	MaxIdleConns        int `mapstructure:"max_idle_connections"`
 	MaxIdleConnsPerHost int `mapstructure:"max_idle_connections_per_host"`
@@ -175,12 +177,13 @@ type FileLogs struct {
 }
 
 type HostCookie struct {
-	Domain       string `mapstructure:"domain"`
-	Family       string `mapstructure:"family"`
-	CookieName   string `mapstructure:"cookie_name"`
-	OptOutURL    string `mapstructure:"opt_out_url"`
-	OptInURL     string `mapstructure:"opt_in_url"`
-	OptOutCookie Cookie `mapstructure:"optout_cookie"`
+	Domain             string `mapstructure:"domain"`
+	Family             string `mapstructure:"family"`
+	CookieName         string `mapstructure:"cookie_name"`
+	OptOutURL          string `mapstructure:"opt_out_url"`
+	OptInURL           string `mapstructure:"opt_in_url"`
+	MaxCookieSizeBytes int    `mapstructure:"max_cookie_size_bytes"`
+	OptOutCookie       Cookie `mapstructure:"optout_cookie"`
 	// Cookie timeout in days
 	TTL int64 `mapstructure:"ttl_days"`
 }
@@ -389,7 +392,7 @@ func New(v *viper.Viper) (*Configuration, error) {
 	}
 	c.setDerivedDefaults()
 
-	// To look for a request's publisher_id into the NonStandardPublishers in
+	// To look for a request's publisher_id in the NonStandardPublishers list in
 	// O(1) time, we fill this hash table located in the NonStandardPublisherMap field of GDPR
 	c.GDPR.NonStandardPublisherMap = make(map[string]int)
 	for i := 0; i < len(c.GDPR.NonStandardPublishers); i++ {
@@ -410,6 +413,11 @@ func New(v *viper.Viper) (*Configuration, error) {
 		c.BlacklistedAcctMap[c.BlacklistedAccts[i]] = true
 	}
 
+	if err := isValidCookieSize(c.HostCookie.MaxCookieSizeBytes); err != nil {
+		glog.Fatal(fmt.Printf("Max cookie size %d cannot be less than %d \n", c.HostCookie.MaxCookieSizeBytes, MIN_COOKIE_SIZE_BYTES))
+		return nil, err
+	}
+
 	glog.Info("Logging the resolved configuration:")
 	logGeneral(reflect.ValueOf(c), "  \t")
 	if errs := c.validate(); len(errs) > 0 {
@@ -525,6 +533,7 @@ func SetupViper(v *viper.Viper, filename string) {
 	v.SetDefault("host_cookie.optout_cookie.name", "")
 	v.SetDefault("host_cookie.value", "")
 	v.SetDefault("host_cookie.ttl_days", 90)
+	v.SetDefault("host_cookie.max_cookie_size_bytes", 0)
 	v.SetDefault("http_client.max_idle_connections", 400)
 	v.SetDefault("http_client.max_idle_connections_per_host", 10)
 	v.SetDefault("http_client.idle_connection_timeout_seconds", 60)
@@ -683,3 +692,12 @@ func setBidderDefaults(v *viper.Viper, bidder string) {
 	v.SetDefault(adapterCfgPrefix+bidder+".disabled", false)
 	v.SetDefault(adapterCfgPrefix+bidder+".partner_id", "")
 }
+
+func isValidCookieSize(maxCookieSize int) error {
+	// If a non-zero-less-than-500-byte "host_cookie.max_cookie_size_bytes" value was specified in the
+	// environment configuration of prebid-server, default to 500 bytes
+	if maxCookieSize != 0 && maxCookieSize < MIN_COOKIE_SIZE_BYTES {
+		return fmt.Errorf("Configured cookie size is less than allowed minimum size of %d \n", MIN_COOKIE_SIZE_BYTES)
+	}
+	return nil
+}
diff --git a/config/config_test.go b/config/config_test.go
index 10ba3258c19..80d278daf08 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -2,6 +2,7 @@ package config
 
 import (
 	"bytes"
+	"fmt"
 	"strings"
 	"testing"
 	"time"
@@ -22,6 +23,7 @@ func TestDefaults(t *testing.T) {
 	cmpInts(t, "auction_timeouts_ms.max", int(cfg.AuctionTimeouts.Max), 0)
 	cmpInts(t, "max_request_size", int(cfg.MaxRequestSize), 1024*256)
 	cmpInts(t, "host_cookie.ttl_days", int(cfg.HostCookie.TTL), 90)
+	cmpInts(t, "host_cookie.max_cookie_size_bytes", cfg.HostCookie.MaxCookieSizeBytes, 0)
 	cmpStrings(t, "datacache.type", cfg.DataCache.Type, "dummy")
 	cmpStrings(t, "adapters.pubmatic.endpoint", cfg.Adapters[string(openrtb_ext.BidderPubmatic)].Endpoint, "http://hbopenbid.pubmatic.com/translator?source=prebid-server")
 	cmpInts(t, "currency_converter.fetch_interval_seconds", cfg.CurrencyConverter.FetchIntervalSeconds, 1800)
@@ -39,6 +41,7 @@ host_cookie:
   domain: cookies.prebid.org
   opt_out_url: http://prebid.org/optout
   opt_in_url: http://prebid.org/optin
+  max_cookie_size_bytes: 32768
 external_url: http://prebid-server.prebid.org/
 host: prebid-server.prebid.org
 port: 1234
@@ -300,6 +303,28 @@ func TestLimitTimeout(t *testing.T) {
 	doTimeoutTest(t, 15, 0, 20, 15)
 }
 
+func TestCookieSizeError(t *testing.T) {
+	type aTest struct {
+		cookieHost  *HostCookie
+		expectError bool
+	}
+	testCases := []aTest{
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: 1 << 15}, expectError: false}, //32 KB, no error
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: 800}, expectError: false},
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: 500}, expectError: false},
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: 0}, expectError: false},
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: 200}, expectError: true},
+		{cookieHost: &HostCookie{MaxCookieSizeBytes: -100}, expectError: true},
+	}
+	for i := range testCases {
+		if testCases[i].expectError {
+			assert.Error(t, isValidCookieSize(testCases[i].cookieHost.MaxCookieSizeBytes), fmt.Sprintf("Configuration.HostCooki.MaxCookieSizeBytes less than MIN_COOKIE_SIZE_BYTES = %d and not equal to zero should return an error", MIN_COOKIE_SIZE_BYTES))
+		} else {
+			assert.NoError(t, isValidCookieSize(testCases[i].cookieHost.MaxCookieSizeBytes), fmt.Sprintf("Configuration.HostCooki.MaxCookieSizeBytes greater than MIN_COOKIE_SIZE_BYTES = %d or equal to zero should not return an error", MIN_COOKIE_SIZE_BYTES))
+		}
+	}
+}
+
 func newDefaultConfig(t *testing.T) *Configuration {
 	v := viper.New()
 	SetupViper(v, "")
diff --git a/endpoints/setuid.go b/endpoints/setuid.go
index 6a17592bd09..0275e354664 100644
--- a/endpoints/setuid.go
+++ b/endpoints/setuid.go
@@ -76,7 +76,7 @@ func NewSetUIDEndpoint(cfg config.HostCookie, perms gdpr.Permissions, pbsanalyti
 			so.Success = true
 		}
 
-		pc.SetCookieOnResponse(w, cfg.Domain, cookieTTL)
+		pc.SetCookieOnResponse(w, &cfg, cookieTTL)
 	})
 }
 
diff --git a/pbs/usersync.go b/pbs/usersync.go
index 8194e7f4ee2..b388d47d1fc 100644
--- a/pbs/usersync.go
+++ b/pbs/usersync.go
@@ -95,7 +95,7 @@ func (deps *UserSyncDeps) OptOut(w http.ResponseWriter, r *http.Request, _ httpr
 	pc := usersync.ParsePBSCookieFromRequest(r, deps.HostCookieConfig)
 	pc.SetPreference(optout == "")
 
-	pc.SetCookieOnResponse(w, deps.HostCookieConfig.Domain, deps.HostCookieConfig.TTLDuration())
+	pc.SetCookieOnResponse(w, deps.HostCookieConfig, deps.HostCookieConfig.TTLDuration())
 	if optout == "" {
 		http.Redirect(w, r, deps.HostCookieConfig.OptInURL, 301)
 	} else {
diff --git a/usersync/cookie.go b/usersync/cookie.go
index a2b773aa2da..7334d15f358 100644
--- a/usersync/cookie.go
+++ b/usersync/cookie.go
@@ -4,6 +4,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"errors"
+	"math"
 	"net/http"
 	"time"
 
@@ -160,11 +161,32 @@ func (cookie *PBSCookie) GetId(bidderName openrtb_ext.BidderName) (id string, ex
 }
 
 // SetCookieOnResponse is a shortcut for "ToHTTPCookie(); cookie.setDomain(domain); setCookie(w, cookie)"
-func (cookie *PBSCookie) SetCookieOnResponse(w http.ResponseWriter, domain string, ttl time.Duration) {
+func (cookie *PBSCookie) SetCookieOnResponse(w http.ResponseWriter, cfg *config.HostCookie, ttl time.Duration) {
 	httpCookie := cookie.ToHTTPCookie(ttl)
+	var domain string = cfg.Domain
+
 	if domain != "" {
 		httpCookie.Domain = domain
 	}
+
+	var currSize int = len([]byte(httpCookie.String()))
+	for cfg.MaxCookieSizeBytes > 0 && currSize > cfg.MaxCookieSizeBytes && len(cookie.uids) > 0 {
+		var oldestElem string = ""
+		var oldestDate int64 = math.MaxInt64
+		for key, value := range cookie.uids {
+			timeUntilExpiration := time.Until(value.Expires)
+			if timeUntilExpiration < time.Duration(oldestDate) {
+				oldestElem = key
+				oldestDate = int64(timeUntilExpiration)
+			}
+		}
+		delete(cookie.uids, oldestElem)
+		httpCookie = cookie.ToHTTPCookie(ttl)
+		if domain != "" {
+			httpCookie.Domain = domain
+		}
+		currSize = len([]byte(httpCookie.String()))
+	}
 	http.SetCookie(w, httpCookie)
 }
 
diff --git a/usersync/cookie_test.go b/usersync/cookie_test.go
index 82cc4f32b9f..2c28956bd87 100644
--- a/usersync/cookie_test.go
+++ b/usersync/cookie_test.go
@@ -67,7 +67,7 @@ func TestBidderNameGets(t *testing.T) {
 func TestRejectAudienceNetworkCookie(t *testing.T) {
 	raw := &PBSCookie{
 		uids: map[string]uidWithExpiry{
-			"audienceNetwork": newTempId("0"),
+			"audienceNetwork": newTempId("0", 10),
 		},
 		optOut:   false,
 		birthday: timestamp(),
@@ -162,7 +162,7 @@ func TestParseOtherCookie(t *testing.T) {
 func TestCookieReadWrite(t *testing.T) {
 	cookie := newSampleCookie()
 
-	received := writeThenRead(cookie)
+	received := writeThenRead(cookie, 0)
 	uid, exists, isLive := received.GetUID("adnxs")
 	if !exists || !isLive || uid != "123" {
 		t.Errorf("Received cookie should have the adnxs ID=123. Got %s", uid)
@@ -262,6 +262,37 @@ func TestGetUIDsWithNilCookie(t *testing.T) {
 	assert.Len(t, uids, 0, "GetUIDs shouldn't return any user syncs for a nil cookie")
 }
 
+func TestTrimCookiesClosestExpirationDates(t *testing.T) {
+	cookieToSend, cookieToSendLen := newTestCookie()
+	closestToExpirationDate := "key7"
+
+	type aTest struct {
+		maxCookieSize int
+		expAction     string
+	}
+	testCases := []aTest{
+		{maxCookieSize: 2000, expAction: "equal"}, //1 don't trim, set
+		{maxCookieSize: 0, expAction: "equal"},    //2 unlimited size: don't trim, set
+		{maxCookieSize: 800, expAction: "trim"},   //3 trim to size and set
+		{maxCookieSize: 500, expAction: "trim"},   //4 trim to size and set
+		{maxCookieSize: 200, expAction: "empty"},  //5 insufficient size, trim to zero lenght and set
+		{maxCookieSize: -100, expAction: "empty"}, //6 invalid size, trim to zero lenght and set
+	}
+	for i := range testCases {
+		processedCookie := writeThenRead(cookieToSend, testCases[i].maxCookieSize)
+		switch testCases[i].expAction {
+		case "equal":
+			assert.Equal(t, cookieToSendLen, len(processedCookie.uids), "[Test %d] MaxCookieSizeBytes equal to zero or bigger than %d bytes should be enough to set and remain cookie unchanged \n", i+1, len(processedCookie.uids))
+			assert.Containsf(t, processedCookie.uids, closestToExpirationDate, "[Test %d] Oldest entry in cookie should not have been eliminated", i+1)
+		case "trim":
+			assert.Equal(t, cookieToSendLen > len(processedCookie.uids), true, "[Test %d] MaxCookieSizeBytes of %d is smaller than %d bytes and cookie entries should have been removed\n", i+1, testCases[i].maxCookieSize, cookieToSendLen)
+			assert.NotContainsf(t, processedCookie.uids, closestToExpirationDate, "[Test %d] Oldest entry in cookie should not have been eliminated", i+1)
+		case "empty":
+			assert.Equal(t, len(processedCookie.uids), 0, "[Test %d] MaxCookieSizeBytes of %d is too small, processedCookie.uids should be empty\n", i+1)
+		}
+	}
+}
+
 func ensureEmptyMap(t *testing.T, cookie *PBSCookie) {
 	if !cookie.AllowSyncs() {
 		t.Error("Empty cookies should allow user syncs.")
@@ -333,31 +364,49 @@ func ensureConsistency(t *testing.T, cookie *PBSCookie) {
 	}
 }
 
-func newTempId(uid string) uidWithExpiry {
+func newTempId(uid string, offset int) uidWithExpiry {
 	return uidWithExpiry{
 		UID:     uid,
-		Expires: time.Now().Add(10 * time.Minute),
+		Expires: time.Now().Add(time.Duration(offset) * time.Minute),
 	}
 }
 
 func newSampleCookie() *PBSCookie {
 	return &PBSCookie{
 		uids: map[string]uidWithExpiry{
-			"adnxs":   newTempId("123"),
-			"rubicon": newTempId("456"),
+			"adnxs":   newTempId("123", 10),
+			"rubicon": newTempId("456", 10),
+		},
+		optOut:   false,
+		birthday: timestamp(),
+	}
+}
+
+func newTestCookie() (*PBSCookie, int) {
+	var mediumSizeCookie *PBSCookie = &PBSCookie{
+		uids: map[string]uidWithExpiry{
+			"key1": newTempId("12345678901234567890123456789012345678901234567890", 7),
+			"key2": newTempId("abcdefghijklmnopqrstuvwxyz", 6),
+			"key3": newTempId("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 6),
+			"key4": newTempId("12345678901234567890123456789612345678901234567890", 5),
+			"key5": newTempId("aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ", 4),
+			"key6": newTempId("12345678901234567890123456789012345678901234567890", 3),
+			"key7": newTempId("abcdefghijklmnopqrstuvwxyz", 2),
 		},
 		optOut:   false,
 		birthday: timestamp(),
 	}
+	return mediumSizeCookie, len(mediumSizeCookie.uids)
 }
 
-func writeThenRead(cookie *PBSCookie) *PBSCookie {
+func writeThenRead(cookie *PBSCookie, maxCookieSize int) *PBSCookie {
 	w := httptest.NewRecorder()
-	cookie.SetCookieOnResponse(w, "mock-domain", 90*24*time.Hour)
+	hostCookie := &config.HostCookie{Domain: "mock-domain", MaxCookieSizeBytes: maxCookieSize}
+	cookie.SetCookieOnResponse(w, hostCookie, 90*24*time.Hour)
 	writtenCookie := w.HeaderMap.Get("Set-Cookie")
 
 	header := http.Header{}
 	header.Add("Cookie", writtenCookie)
 	request := http.Request{Header: header}
-	return ParsePBSCookieFromRequest(&request, &config.HostCookie{})
+	return ParsePBSCookieFromRequest(&request, hostCookie)
 }