In a ten-year study involving 109 renal transplant patients, 37 (34%) developed gastrointestinal complications. The immediate mortality from these complications was 27%. Three of four patients with erosive gastritis died. Five deaths occurred among 17 patients who developed ulcers after transplantation. Emergency surgery for ulcers resulted in two deaths. Patients with peptic ulcer disease, esophagitis, or bleeding before transplantation were much more likely to develop recurrences that patients not so affected. Peptic ulcer occurred notably more often in recipients whose kidneys came from cadavers than from related donors. Experience with gastrointestinal bleeding or its absence during a first transplant is a useful predictor of the results after a second transplant. The high recurrence rate and high mortality suggest that patients with ulcer disease demonstrated before kidney transplantation should either undergo elective surgery for ulcer disease or not be accepted for transplantation. Patients in whom ulcer disease develops after a kidney transplant shoud undergo early elective surgery.