We have reported previously the association between hyposplenism and inflammatory bowel disease. Our study has now been extended to a total of 65 patients with ulcerative colitis and 42 with Crohn's disease so that the incidence of hyposplenism could be more accurately determined. Hyposplenism rarely complicated distal ulcerative colitis, but was found in 15 of 37 patients with total colonic disease. Hyposplenism occurred in 11 out of 31 patients with Crohn's disease of the colon, but in none of 11 individuals with isolated ileal disease. In order to determine whether hyposplenism has any prognostic implications, the peri-operative course of 12 hyposplenic individuals who underwent colectomy was compared with that of 12 controls who required surgery and who had normal splenic function. Four of the hyposplenic subjects became severely shocked after operation and developed disseminated intravascular coagulation. In contrast, the post-operative course in the control patients was uneventful.