Vascular dysplasia is a term which we have used to encompass various congenital vascular malformations of the gastrointestinal tract which are difficult to differentiate and classify on a histologic or clinical basis. Patients with these lesions present with massive hemorrhage or chronic occult bleeding. Conventional barium and endoscopic studies are generally unrevealing and it is difficult for the surgeon to find the dysplasia at laparotomy, which may result in an unsuccessful blind resection. Therefore, angiography, which is the most reliable diagnostic study for detecting these lesions, is indicated prior to laparotomy if the source of bleeding is obscure. Recent publications and our experience suggest that vascular dysplasias are more common in the ascending colon than previously recognized, and special attention should be given to this area during angiographic evaluation.