Massive hemorrhage from the gastrointestinal tract in a 12-yr-old boy caused by a congenital atypically located colonic arteriovenous malformation is described. Guided and "clean" resection of the involved colon was possible due to preoperative selective angiography, which proved to be the most efficient diagnostic tool. Histologic documentation of this rare pathology in childhood is presented, and the classification and features of the disease are briefly reviewed.