Gastrointestinal complications occurred in 19 of 290 recipients (6.6%) of the 325 cadaveric renal allografts undertaken between September 1969 and December 1978. The mortality was 42.1%. Upper gastrointestinal complications, principally haemorrhage, occurred in 12 patients (4.1%), 11 of whom were males, usually within four months of transplantation, and often associated with acute rejection and its treatment. Surgery was required in five patients. The overall mortality was 16.7%. Colonic complications occurred in five patients (1.7%), four of whom died, the absence of specific signs having led to a significant delay in diagnosis. One patient died from abdominal vascular disease, and one from carcinoma of the gallbladder. To decrease the high morbidity and mortality, both medical and appropriate surgical prophylaxis for peptic ulceration and diverticular disease are necessary, as is an awareness of the transplant recipient's propensity to develop a gastrointestinal complication at any time, up to years after transplantation. Early recognition and treatment of such complications are essential.