diff --git a/.changelog/5322.fixed b/.changelog/5322.fixed
new file mode 100644
index 0000000000..26056675fc
--- /dev/null
+++ b/.changelog/5322.fixed
@@ -0,0 +1 @@
+`opentelemetry-instrumentation-aiohttp-server`: capture all values of repeated headers
diff --git a/instrumentation/opentelemetry-instrumentation-aiohttp-server/src/opentelemetry/instrumentation/aiohttp_server/__init__.py b/instrumentation/opentelemetry-instrumentation-aiohttp-server/src/opentelemetry/instrumentation/aiohttp_server/__init__.py
index 99df218557..c7422d7bc0 100644
--- a/instrumentation/opentelemetry-instrumentation-aiohttp-server/src/opentelemetry/instrumentation/aiohttp_server/__init__.py
+++ b/instrumentation/opentelemetry-instrumentation-aiohttp-server/src/opentelemetry/instrumentation/aiohttp_server/__init__.py
@@ -150,7 +150,7 @@ async def hello(request):
 from timeit import default_timer
 
 from aiohttp import web
-from multidict import CIMultiDictProxy
+from multidict import CIMultiDictProxy, MultiMapping
 
 from opentelemetry import metrics, trace
 from opentelemetry.instrumentation._semconv import (
@@ -334,6 +334,13 @@ def collect_request_attributes(
     return result
 
 
+def _get_header_values(headers: MultiMapping[str]) -> dict[str, list[str]]:
+    values: dict[str, list[str]] = {}
+    for key, value in headers.items():
+        values.setdefault(key.lower(), []).append(value)
+    return values
+
+
 def collect_request_headers_attributes(
     request: web.Request,
 ) -> dict[str, list[str]]:
@@ -344,7 +351,7 @@ def collect_request_headers_attributes(
     sanitize = SanitizeValue(get_custom_headers(OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SANITIZE_FIELDS))
 
     return sanitize.sanitize_header_values(
-        request.headers,
+        _get_header_values(request.headers),
         captured_headers,
         normalise_request_header_name,
     )
@@ -353,11 +360,15 @@ def collect_request_headers_attributes(
 def collect_response_headers_attributes(
     response: web.Response,
 ) -> dict[str, list[str]]:
+    captured_headers = get_custom_headers(OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE)
+    if not captured_headers:
+        return {}
+
     sanitize = SanitizeValue(get_custom_headers(OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SANITIZE_FIELDS))
 
     return sanitize.sanitize_header_values(
-        response.headers,
-        get_custom_headers(OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE),
+        _get_header_values(response.headers),
+        captured_headers,
         normalise_response_header_name,
     )
 
diff --git a/instrumentation/opentelemetry-instrumentation-aiohttp-server/tests/test_aiohttp_server_integration.py b/instrumentation/opentelemetry-instrumentation-aiohttp-server/tests/test_aiohttp_server_integration.py
index a49c72e4cc..3313b85cd3 100644
--- a/instrumentation/opentelemetry-instrumentation-aiohttp-server/tests/test_aiohttp_server_integration.py
+++ b/instrumentation/opentelemetry-instrumentation-aiohttp-server/tests/test_aiohttp_server_integration.py
@@ -561,6 +561,38 @@ async def test_custom_request_headers_control_sampling(
     assert len(exporter.get_finished_spans()) == expected_span_count
 
 
+@pytest.mark.asyncio
+async def test_custom_request_headers_repeated(test_base: TestBase, aiohttp_server, monkeypatch):
+    expected = {
+        "http.request.header.custom_test_header_1": ["test-header-value-1", "test-header-value-2"],
+        "http.request.header.my_secret_header": ["[REDACTED]", "[REDACTED]"],
+    }
+    sampler = CapturingSampler()
+    server, exporter = await _create_server_with_sampler(aiohttp_server, monkeypatch, sampler)
+
+    try:
+        url = f"http://{server.host}:{server.port}/status/200"
+        async with aiohttp.ClientSession() as session:
+            headers = CIMultiDict(
+                [
+                    ("custom-test-header-1", "test-header-value-1"),
+                    ("custom-test-header-1", "test-header-value-2"),
+                    ("My-Secret-Header", "My Secret Value 1"),
+                    ("My-Secret-Header", "My Secret Value 2"),
+                ]
+            )
+            async with session.get(url, headers=headers) as response:
+                assert response.status == 200
+    finally:
+        AioHttpServerInstrumentor().uninstrument()
+
+    assert _request_header_attributes(sampler.attributes) == expected
+
+    spans = exporter.get_finished_spans()
+    assert len(spans) == 1
+    assert _request_header_attributes(spans[0].attributes) == {key: tuple(value) for key, value in expected.items()}
+
+
 @pytest.mark.asyncio
 async def test_custom_response_headers(test_base: TestBase, aiohttp_server, monkeypatch):
     monkeypatch.setenv(
@@ -617,6 +649,46 @@ async def handler(request):
     AioHttpServerInstrumentor().uninstrument()
 
 
+@pytest.mark.asyncio
+async def test_custom_response_headers_repeated(test_base: TestBase, aiohttp_server, monkeypatch):
+    monkeypatch.setenv(
+        OTEL_INSTRUMENTATION_HTTP_CAPTURE_HEADERS_SERVER_RESPONSE,
+        "Custom-Test-Header-1",
+    )
+    AioHttpServerInstrumentor().instrument()
+
+    app = aiohttp.web.Application()
+
+    async def handler(request):
+        headers = CIMultiDict(
+            [
+                ("custom-test-header-1", "test-header-value-1"),
+                ("Custom-Test-Header-1", "test-header-value-2"),
+            ]
+        )
+        return aiohttp.web.Response(text="hello", headers=headers)
+
+    app.router.add_get("/status/200", handler)
+
+    server = await aiohttp_server(app)
+
+    url = f"http://{server.host}:{server.port}/status/200"
+    async with aiohttp.ClientSession() as session:
+        async with session.get(url) as response:
+            assert response.status == 200
+            assert await response.text() == "hello"
+
+    spans = test_base.get_finished_spans()
+    assert len(spans) == 1
+
+    assert spans[0].attributes.get("http.response.header.custom_test_header_1") == (
+        "test-header-value-1",
+        "test-header-value-2",
+    )
+
+    AioHttpServerInstrumentor().uninstrument()
+
+
 # pylint: disable=too-many-locals
 @pytest.mark.asyncio
 async def test_semantic_conventions_metrics_old_default(test_base: TestBase, aiohttp_server, monkeypatch):