The Roux-en-Y gastric bypass is one of the most extensive surgical treatments for obesity. The treatment of upper gastrointestinal bleeding after Roux-en-Y gastric bypass is complex due to the difficulty of accessing the excluded gastric antrum and duodenal bulb. There is no consensus regarding the management of this complication. While various techniques have been described to access the biliopancreatic limb, double-balloon enteroscopy is the most commonly used. If double-balloon enteroscopy is unavailable, a pediatric colonoscope may be used as an alternative; however, its use in such cases has not been described. We report the case of a 50-year-old male patient who underwent gastric bypass 13 years ago and was admitted for a second episode of upper gastrointestinal bleeding. The initial approach using upper endoscopy, colonoscopy, and abdominal computed tomography angiography did not reveal the cause of gastrointestinal hemorrhage; therefore, an endoscopic study of the biliopancreatic limb was performed using a pediatric colonoscope. A Forrest Ib ulcer was found in the duodenal bulb, and endoscopic therapy was administered. The evolution was found to be satisfactory. Clin Endosc 2021 May 25.