Twenty-one of fifteen hundred twenty-six patients with Crohn's disease (CD) treated at The Mount Sinai Hospital between 1960 and 1986 developed severe gastrointestinal hemorrhage. There were 26 separate episodes of severe hemorrhage: 17 patients bled only once, three bled twice, and one bled three times. The frequency of bleeding was significantly higher among patients with colonic involvement (17 of 929; 1.9%) than among those with small bowel disease alone (4 of 597; 0.7%) (p < 0.001). Twelve patients required surgery on 13 occasions, which involved colon resection in all but one case. Eleven of these patients underwent surgery during their first hemorrhagic episodes, and 1 of 11 had a second operation for recurrent bleeding; the 12th patient, whose first hemorrhage had been treated medically, had surgery during a repeated episode of hemorrhage. The precise bleeding points could be located in only 2 of the 26 bleeding episodes, both at the ileocecal area. Three patients died, of whom two had not undergone surgery when they had bled a few weeks earlier. Primary bleeding episodes subsided without surgery in 10 of 21 cases, but 3 of these 10 patients (30%) rebled massively. By contrast primary excisional surgery was followed by recurrent hemorrhage in only 1 of 11 cases (9%). These differences in mortality and in recurrent bleeding rates, although not statistically significant, seem to favor removal of diseased bowel at the time of the first episode of massive hemorrhage.