diff --git a/x-pack/plugins/apm/public/components/app/TransactionOverview/index.tsx b/x-pack/plugins/apm/public/components/app/TransactionOverview/index.tsx
index 9018fbb2bc410..b5f91c7fdeb54 100644
--- a/x-pack/plugins/apm/public/components/app/TransactionOverview/index.tsx
+++ b/x-pack/plugins/apm/public/components/app/TransactionOverview/index.tsx
@@ -11,6 +11,9 @@ import {
   EuiFlexGroup,
   EuiFlexItem,
   EuiHorizontalRule,
+  EuiCallOut,
+  EuiLink,
+  EuiCode,
 } from '@elastic/eui';
 import { Location } from 'history';
 import { first } from 'lodash';
@@ -154,6 +157,20 @@ export function TransactionOverview() {
               <h3>Transactions</h3>
             </EuiTitle>
             <EuiSpacer size="s" />
+            <EuiCallOut
+              title="This view shows a subset of reported transactions."
+              color="danger"
+              iconType="alert"
+            >
+              <p>
+                The number of unique transaction names exceeds the configured
+                value of 200. Try reconfiguring your agents to group similar
+                transactions or increase the value of
+                <EuiCode>xpack.apm.ui.transactionGroupBucketSize</EuiCode>.{' '}
+                <EuiLink href="#">Learn more in the docs.</EuiLink>.
+              </p>
+            </EuiCallOut>
+            <EuiSpacer size="s" />
             <TransactionList
               isLoading={transactionListStatus === 'loading'}
               items={transactionListData}