diff --git a/index.js b/index.js
index 068126b..6bf783e 100644
--- a/index.js
+++ b/index.js
@@ -6,7 +6,7 @@ import { microsubController } from "./lib/controllers/microsub.js";
 import { readerController } from "./lib/controllers/reader.js";
 import { handleMediaProxy } from "./lib/media/proxy.js";
 import { startScheduler, stopScheduler } from "./lib/polling/scheduler.js";
-import { createIndexes } from "./lib/storage/items.js";
+import { cleanupAllReadItems, createIndexes } from "./lib/storage/items.js";
 import { webmentionReceiver } from "./lib/webmention/receiver.js";
 import { websubHandler } from "./lib/websub/handler.js";
 
@@ -157,6 +157,11 @@ export default class MicrosubEndpoint {
       createIndexes(indiekit).catch((error) => {
         console.warn("[Microsub] Index creation failed:", error.message);
       });
+
+      // Cleanup old read items on startup
+      cleanupAllReadItems(indiekit).catch((error) => {
+        console.warn("[Microsub] Startup cleanup failed:", error.message);
+      });
     } else {
       console.warn(
         "[Microsub] Database not available at init, scheduler not started",
diff --git a/lib/storage/items.js b/lib/storage/items.js
index 002762b..ed6d7ab 100644
--- a/lib/storage/items.js
+++ b/lib/storage/items.js
@@ -328,6 +328,68 @@ async function cleanupOldReadItems(collection, channelObjectId, userId) {
   }
 }
 
+/**
+ * Cleanup all read items across all channels (startup cleanup)
+ * @param {object} application - Indiekit application
+ * @returns {Promise<number>} Total number of items deleted
+ */
+export async function cleanupAllReadItems(application) {
+  const collection = getCollection(application);
+  const channelsCollection = application.collections.get("microsub_channels");
+
+  // Get all channels
+  const channels = await channelsCollection.find({}).toArray();
+  let totalDeleted = 0;
+
+  for (const channel of channels) {
+    // Get unique userIds who have read items in this channel
+    const readByUsers = await collection.distinct("readBy", {
+      channelId: channel._id,
+      readBy: { $exists: true, $ne: [] },
+    });
+
+    for (const userId of readByUsers) {
+      if (!userId) continue;
+
+      const readCount = await collection.countDocuments({
+        channelId: channel._id,
+        readBy: userId,
+      });
+
+      if (readCount > MAX_READ_ITEMS) {
+        const itemsToDelete = await collection
+          .find({
+            channelId: channel._id,
+            readBy: userId,
+          })
+          .sort({ published: -1, _id: -1 })
+          .skip(MAX_READ_ITEMS)
+          .project({ _id: 1 })
+          .toArray();
+
+        if (itemsToDelete.length > 0) {
+          const idsToDelete = itemsToDelete.map((item) => item._id);
+          const deleteResult = await collection.deleteMany({
+            _id: { $in: idsToDelete },
+          });
+          totalDeleted += deleteResult.deletedCount;
+          console.info(
+            `[Microsub] Startup cleanup: deleted ${deleteResult.deletedCount} old items from channel "${channel.name}"`,
+          );
+        }
+      }
+    }
+  }
+
+  if (totalDeleted > 0) {
+    console.info(
+      `[Microsub] Startup cleanup complete: ${totalDeleted} total items deleted`,
+    );
+  }
+
+  return totalDeleted;
+}
+
 export async function markItemsRead(application, channelId, entryIds, userId) {
   const collection = getCollection(application);
   const channelObjectId =
diff --git a/package.json b/package.json
index d5857f2..fa5ceb8 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rmdes/indiekit-endpoint-microsub",
-  "version": "1.0.21",
+  "version": "1.0.22",
   "description": "Microsub endpoint for Indiekit. Enables subscribing to feeds and reading content using the Microsub protocol.",
   "keywords": [
     "indiekit",