In 277 consecutive renal transplantations, 49 of 254 patients (19%) developed a gastrointestinal complication causing a mortality rate of 29% (14/49 patients). Oesophageal, gastro-duodenal, pancreatic and ileocolonic complications are reviewed and discussed. Acute gastro-duodenal ulcerations proved to be the most common problem (45--22/49 patients). The loss of allograft in this group of 22 patients was 42% (9/22 patients). To overcome their high mortality (27%--6/22 patients) efforts were made to prevent these complications. After introduction of prophylactic surgery, mortality dropped from 4 to 2%, after systematic long-term prophylactic use of cimetidine, mortality even dropped to 0%. In this last series of 52 patients only one bleeding ulcer was seen immediately after allograft nephrectomy. Ileocolonic complications in renal transplant patients, difficult to diagnose and treat, are associated with a high morbidity and lethality. In 6 patients with colonic complications, 4 could be saved by early and aggressive surgery (67% survival rate). Two recipients developed a de novo gastrointestinal malignancy. Early, accurate, diagnosis and surgical therapy of gastro-intestinal complications after renal transplantation are directly related to the graft and/or patient survival rate. Every effort is therefore necessary to prevent these complications.