diff --git a/packages/backend/src/server/api/endpoints/users/following.ts b/packages/backend/src/server/api/endpoints/users/following.ts
index 084d278095..3dd150c5ad 100644
--- a/packages/backend/src/server/api/endpoints/users/following.ts
+++ b/packages/backend/src/server/api/endpoints/users/following.ts
@@ -66,11 +66,6 @@ export const paramDef = {
 			nullable: true,
 			description: 'The local host is represented with `null`.',
 		},
-
-		birthday: {
-			...birthdaySchema, nullable: true,
-			description: '@deprecated use get-following-birthday-users instead.',
-		},
 	},
 	anyOf: [
 		{ required: ['userId'] },
@@ -129,20 +124,6 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				.andWhere('following.followerId = :userId', { userId: user.id })
 				.innerJoinAndSelect('following.followee', 'followee');
 
-			// @deprecated use get-following-birthday-users instead.
-			if (ps.birthday) {
-				query.innerJoin(this.userProfilesRepository.metadata.targetName, 'followeeProfile', 'followeeProfile.userId = following.followeeId');
-
-				try {
-					const birthday = ps.birthday.split('-');
-					birthday.shift(); // 年の部分を削除
-					// なぜか get_birthday_date() = :birthday だとインデックスが効かないので、BETWEEN で対応
-					query.andWhere('get_birthday_date(followeeProfile.birthday) BETWEEN :birthday AND :birthday', { birthday: parseInt(birthday.join('')) });
-				} catch (err) {
-					throw new ApiError(meta.errors.birthdayInvalid);
-				}
-			}
-
 			const followings = await query
 				.limit(ps.limit)
 				.getMany();
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 9182cf6924..5cc9fa5e72 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -24430,8 +24430,6 @@ export type operations = {
           username?: string;
           /** @description The local host is represented with `null`. */
           host?: string | null;
-          /** @description @deprecated use get-following-birthday-users instead. */
-          birthday?: string | null;
         };
       };
     };