Endoscopy to evaluate upper gastrointestinal bleeding was done for 482 patients over a 42-month period. Fifty-nine patients (12%) had chronic renal failure and upper gastrointestinal bleeding; the remaining 423 did not have renal failure. Angiodysplasia of the stomach or duodenum was the most frequent source of bleeding in patients with renal failure. Angiodysplasia (p less than 0.001) and erosive esophagitis (p less than 0.01) were significantly commoner causes of bleeding in the renal failure population than in the group without renal failure. Recurrent bleeding was also more frequent in patients with renal failure (25%) than in the other patients (11%). Angiodysplasia was the most frequent source of recurrent bleeding in patients with renal failure (53%) whereas peptic lesions were the most likely sources in those without renal failure (51%). These data show that the differential diagnoses of first and subsequent upper gastrointestinal bleeding sites differ for patients with and without chronic renal failure.