Introduction <p>With the rising number of MBS and their revisions, rare complications may start to increase as well. Iatrogenic diaphragmatic hernia following metabolic and bariatric surgery (MBS) is extremely rare but potentially fatal. Its recognition is often delayed due to vague clinical presentations.</p> Purpose <p>We report a case of strangulated diaphragmatic hernia after Roux-en-Y gastric bypass (RYGB) and gastro-gastric fistula dismantling, highlighting diagnostic and surgical pitfalls, and lessons for bariatric surgeons.</p> Methods <p>We describe the presentation, diagnostic work-up, and surgical management of a diaphragmatic hernia after RYGB.</p> Results <p>The patient had a smooth postoperative recovery but then developed pleural effusion requiring tapping. She had recovered fully with normal follow-up clinically and radiologically.</p> Conclusion <p>This case highlights the importance of attention to such rare but life-threatening consequences after MBS. Precise use of energy devices intraoperatively, especially in revisional cases, is mandatory. A high index of suspicion for vague abdominal symptoms and tailored surgical strategies are essential.</p>