Gastric adenocarcinoma after gastric bypass for morbid obesity is rare but has been described. The diet restriction, weight loss, and difficult assessment of the bypassed stomach, after this procedure, hinder and delay its diagnosis. We present a 52-year-old man who underwent Roux-en-Y gastric bypass 2 years ago and whose previous upper digestive endoscopy was considered normal. He presented with weight loss, attributed to the procedure, and progressive dysphagia. Upper digestive endoscopy revealed stenosing tumor in gastric pouch whose biopsy showed diffuse-type gastric adenocarcinoma. He underwent total gastrectomy, left lobectomy, distal pancreatectomy and splenectomy, segmental colectomy, and bowel resection with esophagojejunal anastomosis. The histopathological analysis confirmed the presence of gastric cancer. The pathogenesis of gastric pouch adenocarcinoma is discussed with a literature review.