Massive gastrointestinal bleeding is a very rare complication in Crohn's disease. Its occurrence has been quoted as 1-2% in the literature. A case of a 16-year old boy is reported here, who had a three-year history of Crohn's disease. After a three-day's therapy of bronchopneumonia a massive rectal bleeding began and an emergency operation had to be made. Site of the bleeding was localised by intraoperative colonoscopy and an ileocolic resection was made. The patient recovered and has done well since. Some characteristics, diagnostic and therapeutic problems of the massive bleeding in Crohn's disease are discussed.