Over a 3-year period, arteriovenous malformations (angiodysplasia) were identified at upper gastrointestinal endoscopy in 41 patients. The lesions were multiple in one-third of patients and were predominantly situated in the proximal stomach. We considered angiodysplasia to be the cause of upper gastrointestinal bleeding in 11 (27%) patients and of anemia in nine (22%) patients. In these two groups other mucosal lesions were not seen at upper gastrointestinal endoscopy and there had been prior undiagnosed episodes of overt or occult bleeding in almost half. In 21 (51%) patients the lesions were judged to be incidental findings. Other medical conditions noted were the presence of an aortic systolic murmur (24%) and renal impairment (12%). Only three patients had mucocutaneous telangiectasia (two had Osler-Rendu-Weber syndrome, and one had scleroderma with CRST syndrome). Specific treatment in 14 symptomatic patients included endoscopic electrocoagulation or injection sclerotherapy. In eight patients with adequate post-treatment surveillance, endoscopy demonstrated obliteration of the vascular lesions.