Among the techniques available for bariatric surgery, Roux-en-Y gastric bypass is safe and effective option. However, it may present with some complications such as marginal anasomotic ulcers, which can perforate and become serious surgical emergency.We present a case of 28-year-old female patient, with abdominal pain and vomiting with clinical presentation of diffuse peritonitis, radiological presentation of pneumoperitoneum and medical history of RYGB 3 years before, with suspected perforation after initial medical assessment and examination. Upper medial laparotomy was performed with large amount of fibrinopurulent content presented in abdominal cavity and perforated MU at medial anastomotic site. It was closed with omental patch, after thorough abdominal irrigation. The patient was discharged on the 10th day after surgery.One of the most common long-term complications after RYGB is the occurence of peptic ulcers and anastomotic stenosis. The main manifestation of untreated MU is perforation, which is urgent surgical and life-threatening condition. The perforated marginal ulcer is a complication of the RYGB procedure in bariatric surgery and is an acute surgical condition. Thorough irrigation of abdominal cavity and omentoplasty of the ulcer lesion is a safe and effective treatment of choice and it gives a good postoperative outcome.