diff --git a/README.md b/README.md
index b2f72de..131f0b9 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,6 @@
 deciles-charts generates a line chart for each [measure table][1] in an input directory.
 The line chart has time on the horizontal axis (`x`) and value on the vertical axis (`y`).
 Deciles are plotted as dashed lines;
-outer percentiles are plotted as dotted lines;
 the median is plotted as a solid line.
 For example, the following deciles chart was generated from dummy data:
 
@@ -68,6 +67,29 @@ For each measure table, there will now be a corresponding deciles chart.
 For example, given a measure table called `measure_has_sbp_event_by_stp_code.csv`,
 there will now be a corresponding deciles chart called `deciles_chart_has_sbp_event_by_stp_code.png`.
 
+## Configuration
+
+Pass configuration via the `config` property.
+For example:
+
+```yaml
+generate_deciles_charts:
+  run: >
+    deciles-charts:[version]
+      --input-files output/measure_*.csv
+      --output_dir output
+  config:
+    show_outer_percentiles: true
+  needs: [generate_measures]
+  outputs:
+    moderately_sensitive:
+      deciles_charts: output/deciles_chart_*.png
+```
+
+| Configuration            | Default | Description                                                 |
+| ------------------------ | ------- | ----------------------------------------------------------- |
+| `show_outer_percentiles` | `false` | Show the top and bottom percentiles, as well as the deciles |
+
 ## Notes for developers
 
 Please see [_DEVELOPERS.md_](DEVELOPERS.md).
diff --git a/analysis/deciles_charts.py b/analysis/deciles_charts.py
index b219250..e056494 100644
--- a/analysis/deciles_charts.py
+++ b/analysis/deciles_charts.py
@@ -1,5 +1,6 @@
 import argparse
 import glob
+import json
 import logging
 import pathlib
 import re
@@ -9,6 +10,10 @@
 from ebmdatalab import charts
 
 
+DEFAULT_CONFIG = {
+    "show_outer_percentiles": False,
+}
+
 MEASURE_FNAME_REGEX = re.compile(r"measure_(?P<id>\w+)\.csv")
 
 # replicate cohort-extractor's logging
@@ -51,8 +56,13 @@ def drop_zero_denominator_rows(measure_table):
     return measure_table[is_not_inf].reset_index(drop=True)
 
 
-def get_deciles_chart(measure_table):
-    return charts.deciles_chart(measure_table, period_column="date", column="value")
+def get_deciles_chart(measure_table, config):
+    return charts.deciles_chart(
+        measure_table,
+        period_column="date",
+        column="value",
+        show_outer_percentiles=config["show_outer_percentiles"],
+    )
 
 
 def write_deciles_chart(deciles_chart, path):
@@ -67,6 +77,17 @@ def match_paths(pattern):
     return [get_path(x) for x in glob.glob(pattern)]
 
 
+def parse_config(config_json):
+    user_config = json.loads(config_json)
+    config = DEFAULT_CONFIG.copy()
+    if invalid_keys := [k for k in user_config if k not in config]:
+        invalid_keys_str = ", ".join(invalid_keys)
+        raise RuntimeError(f"Invalid configuration: {invalid_keys_str}")
+
+    config.update(user_config)
+    return config
+
+
 def parse_args():
     parser = argparse.ArgumentParser()
     parser.add_argument(
@@ -81,6 +102,12 @@ def parse_args():
         type=get_path,
         help="Path to the output directory",
     )
+    parser.add_argument(
+        "--config",
+        default=DEFAULT_CONFIG.copy(),
+        type=parse_config,
+        help="JSON-encoded configuration",
+    )
     return parser.parse_args()
 
 
@@ -88,10 +115,11 @@ def main():
     args = parse_args()
     input_files = args.input_files
     output_dir = args.output_dir
+    config = args.config
 
     for measure_table in get_measure_tables(input_files):
         measure_table = drop_zero_denominator_rows(measure_table)
-        chart = get_deciles_chart(measure_table)
+        chart = get_deciles_chart(measure_table, config)
         id_ = measure_table.attrs["id"]
         fname = f"deciles_chart_{id_}.png"
         write_deciles_chart(chart, output_dir / fname)
diff --git a/img/deciles_chart_has_sbp_event_by_stp_code.png b/img/deciles_chart_has_sbp_event_by_stp_code.png
index 4b6bc91..9277cd0 100644
Binary files a/img/deciles_chart_has_sbp_event_by_stp_code.png and b/img/deciles_chart_has_sbp_event_by_stp_code.png differ
diff --git a/tests/test_deciles_charts.py b/tests/test_deciles_charts.py
index 9b6b0ee..74d0c8f 100644
--- a/tests/test_deciles_charts.py
+++ b/tests/test_deciles_charts.py
@@ -1,5 +1,6 @@
 import numpy
 import pandas
+import pytest
 from pandas import testing
 
 from analysis import deciles_charts
@@ -75,7 +76,25 @@ def test_drop_zero_denominator_rows():
     assert obs_measure_table.attrs is not measure_table.attrs  # test it's a copy
 
 
-def test_parse_args(tmp_path, monkeypatch):
+def test_parse_config():
+    with pytest.raises(RuntimeError, match=r"bad_key, worse_key$"):
+        deciles_charts.parse_config('{"bad_key": "", "worse_key": ""}')
+
+
+@pytest.mark.parametrize(
+    "optional_arg,parsed_optional_arg",
+    [
+        (
+            (),
+            ("config", {"show_outer_percentiles": False}),  # default
+        ),
+        (
+            ("--config", '{"show_outer_percentiles": true}'),
+            ("config", {"show_outer_percentiles": True}),
+        ),
+    ],
+)
+def test_parse_args(tmp_path, monkeypatch, optional_arg, parsed_optional_arg):
     # arrange
     monkeypatch.chdir(tmp_path)
     monkeypatch.setattr(
@@ -86,7 +105,8 @@ def test_parse_args(tmp_path, monkeypatch):
             "input/measure_*.csv",
             "--output-dir",
             "output",
-        ],
+        ]
+        + list(optional_arg),
     )
 
     input_dir = tmp_path / "input"
@@ -115,3 +135,4 @@ def test_parse_args(tmp_path, monkeypatch):
     # assert
     assert sorted(args.input_files) == sorted(input_files)
     assert args.output_dir == output_dir
+    assert getattr(args, parsed_optional_arg[0]) == parsed_optional_arg[1]