BACKGROUND Ectopic or heterotopic pancreas is relatively rare pathology described as pancreatic tissue lacking communication with the normal pancreas. Ectopic pancreatic tissue can be found along the gastrointestinal tract, with the most common location the stomach along the greater curvature. This congenital condition could be identified incidentally, or present with symptoms that range from pain and bleeding to obstruction and malignant transformation. CASE REPORT We report a case of a 30-year-old female, who underwent laparoscopic sleeve gastrectomy for morbid obesity of body mass index (BMI) of 46 kg/m², and who was found to have a 3 cm submucosal mass at the lesser curvature while dividing the stomach. The sleeved stomach tube's intraoperative gastroscopy showed a submucosal mass at the posterior stomach wall towards the lesser curvature, increasing the suspicion of gastrointestinal stromal tumor (GIST) tumor. The choice was to continue with a secure margin and conversion to roux-en-y gastric bypass with gastric tumor resection. It turned out that the final pathology was submucosal ectopic pancreas. Despite being a rare pathology, for any submucosal gastric mass, ectopic pancreas should be on the differential diagnosis list. During the sleeve surgery, the mass was found, and the approach was changed to intraoperatively subtotal gastrectomy and roux-en-y gastric bypass. CONCLUSIONS Before any bariatric operation, even in asymptomatic young patients, it is worth doing routine upper endoscopy to prevent surprising intraoperative pathology.