Postoperative pain after mastectomy remains a significant clinical problem that may impair patient comfort and delay early rehabilitation, potentially affecting functional recovery. Various analgesic techniques are used to manage postoperative pain. This study aims to compare serratus posterior superior intercostal plane block and erector spinae plane block, which are routinely used in our clinic for postoperative analgesia in patients undergoing mastectomy, in terms of ease of application and patient comfort.