diff --git a/include/zephyr/bluetooth/bluetooth.h b/include/zephyr/bluetooth/bluetooth.h
index 3a3409ecf0a..202d29eb9ca 100644
--- a/include/zephyr/bluetooth/bluetooth.h
+++ b/include/zephyr/bluetooth/bluetooth.h
@@ -1822,8 +1822,11 @@ int bt_le_per_adv_sync_delete(struct bt_le_per_adv_sync *per_adv_sync);
  * such as synced, terminated and when data is received.
  *
  * @param cb Callback struct. Must point to memory that remains valid.
+ *
+ * @retval 0 Success.
+ * @retval -EEXIST if @p cb was already registered.
  */
-void bt_le_per_adv_sync_cb_register(struct bt_le_per_adv_sync_cb *cb);
+int bt_le_per_adv_sync_cb_register(struct bt_le_per_adv_sync_cb *cb);
 
 /**
  * @brief Enables receiving periodic advertising reports for a sync.
@@ -2309,8 +2312,11 @@ int bt_le_scan_stop(void);
  * API was used to start the scanner.
  *
  * @param cb Callback struct. Must point to memory that remains valid.
+ *
+ * @retval 0 Success.
+ * @retval -EEXIST if @p cb was already registered.
  */
-void bt_le_scan_cb_register(struct bt_le_scan_cb *cb);
+int bt_le_scan_cb_register(struct bt_le_scan_cb *cb);
 
 /**
  * @brief Unregister scanner packet callbacks.
diff --git a/include/zephyr/bluetooth/conn.h b/include/zephyr/bluetooth/conn.h
index c3c2fb06cfe..9b7f4d9153b 100644
--- a/include/zephyr/bluetooth/conn.h
+++ b/include/zephyr/bluetooth/conn.h
@@ -1256,8 +1256,11 @@ struct bt_conn_cb {
  *  Register callbacks to monitor the state of connections.
  *
  *  @param cb Callback struct. Must point to memory that remains valid.
+ *
+ * @retval 0 Success.
+ * @retval -EEXIST if @p cb was already registered.
  */
-void bt_conn_cb_register(struct bt_conn_cb *cb);
+int bt_conn_cb_register(struct bt_conn_cb *cb);
 
 /**
  * @brief Unregister connection callbacks.
diff --git a/include/zephyr/bluetooth/testing.h b/include/zephyr/bluetooth/testing.h
index 58aae9726ff..74806a53a6d 100644
--- a/include/zephyr/bluetooth/testing.h
+++ b/include/zephyr/bluetooth/testing.h
@@ -53,8 +53,11 @@ struct bt_test_cb {
 /** Register callbacks for Bluetooth testing purposes
  *
  *  @param cb bt_test_cb callback structure
+ *
+ * @retval 0 Success.
+ * @retval -EEXIST if @p cb was already registered.
  */
-void bt_test_cb_register(struct bt_test_cb *cb);
+int bt_test_cb_register(struct bt_test_cb *cb);
 
 /** Unregister callbacks for Bluetooth testing purposes
  *
diff --git a/subsys/bluetooth/host/conn.c b/subsys/bluetooth/host/conn.c
index af70be35cc8..1b2117058e5 100644
--- a/subsys/bluetooth/host/conn.c
+++ b/subsys/bluetooth/host/conn.c
@@ -2508,11 +2508,15 @@ bt_security_t bt_conn_get_security(const struct bt_conn *conn)
 }
 #endif /* CONFIG_BT_SMP */
 
-void bt_conn_cb_register(struct bt_conn_cb *cb)
+int bt_conn_cb_register(struct bt_conn_cb *cb)
 {
-	if (!sys_slist_find(&conn_cbs, &cb->_node, NULL)) {
-		sys_slist_append(&conn_cbs, &cb->_node);
+	if (sys_slist_find(&conn_cbs, &cb->_node, NULL)) {
+		return -EEXIST;
 	}
+
+	sys_slist_append(&conn_cbs, &cb->_node);
+
+	return 0;
 }
 
 int bt_conn_cb_unregister(struct bt_conn_cb *cb)
diff --git a/subsys/bluetooth/host/scan.c b/subsys/bluetooth/host/scan.c
index c7ac96b0e85..65868e941a0 100644
--- a/subsys/bluetooth/host/scan.c
+++ b/subsys/bluetooth/host/scan.c
@@ -1586,11 +1586,15 @@ int bt_le_scan_stop(void)
 	return bt_le_scan_update(false);
 }
 
-void bt_le_scan_cb_register(struct bt_le_scan_cb *cb)
+int bt_le_scan_cb_register(struct bt_le_scan_cb *cb)
 {
-	if (!sys_slist_find(&scan_cbs, &cb->node, NULL)) {
-		sys_slist_append(&scan_cbs, &cb->node);
+	if (sys_slist_find(&scan_cbs, &cb->node, NULL)) {
+		return -EEXIST;
 	}
+
+	sys_slist_append(&scan_cbs, &cb->node);
+
+	return 0;
 }
 
 void bt_le_scan_cb_unregister(struct bt_le_scan_cb *cb)
@@ -1833,11 +1837,15 @@ int bt_le_per_adv_sync_delete(struct bt_le_per_adv_sync *per_adv_sync)
 	return err;
 }
 
-void bt_le_per_adv_sync_cb_register(struct bt_le_per_adv_sync_cb *cb)
+int bt_le_per_adv_sync_cb_register(struct bt_le_per_adv_sync_cb *cb)
 {
-	if (!sys_slist_find(&pa_sync_cbs, &cb->node, NULL)) {
-		sys_slist_append(&pa_sync_cbs, &cb->node);
+	if (sys_slist_find(&pa_sync_cbs, &cb->node, NULL)) {
+		return -EEXIST;
 	}
+
+	sys_slist_append(&pa_sync_cbs, &cb->node);
+
+	return 0;
 }
 
 static int bt_le_set_per_adv_recv_enable(
diff --git a/subsys/bluetooth/host/testing.c b/subsys/bluetooth/host/testing.c
index 690708fadc5..16fb15b94e6 100644
--- a/subsys/bluetooth/host/testing.c
+++ b/subsys/bluetooth/host/testing.c
@@ -20,11 +20,15 @@
 
 static sys_slist_t cb_slist;
 
-void bt_test_cb_register(struct bt_test_cb *cb)
+int bt_test_cb_register(struct bt_test_cb *cb)
 {
-	if (!sys_slist_find(&cb_slist, &cb->node, NULL)) {
-		sys_slist_append(&cb_slist, &cb->node);
+	if (sys_slist_find(&cb_slist, &cb->node, NULL)) {
+		return -EEXIST;
 	}
+
+	sys_slist_append(&cb_slist, &cb->node);
+
+	return 0;
 }
 
 void bt_test_cb_unregister(struct bt_test_cb *cb)