Five hundred and one patients with Crohn's disease, presenting to a single surgical unit during a 20-year period, were reviewed by utilizing a computerized audit system. Ten patients were identified with rectal bleeding significant enough to require a blood transfusion to maintain cardiovascular homeostasis. The site of bleeding was correctly identified pre-operatively in only one patient, and at the time of surgery in only four patients. In nine (90%) of the 10 cases, the origin of the bleeding was subsequently found to be colonic. All 10 patients were treated surgically, with seven patients requiring fashioning of a stoma, none of whom had gastro-intestinal continuity subsequently re-established. Recurrent bleeding occurred in a single patient. The early post-operative mortality was 20%. Massive rectal bleeding remains an uncommon complication of Crohn's disease, and still carries significant morbidity and mortality. Pre-operative localization of the site of bleeding is uncommon, making intra-operative identification of the bleeding area difficult.