An ileosigmoid fistula complicating Crohn's disease of the small bowel has been considered a perplexing entity, but in practice does not pose a serious operative problem. The presence of such a fistula does not signify that the sigmoid colon is a primary site of Crohn's disease. The operative treatment of this entity is simple and usually does not require resection of the sigmoid colon. Rather the sigmoid colon defect may easily be treated by simple closure, or by minimal partial resection and closure. Temporary diversion of the fecal stream is occasionally indicated because of local inflammation. Forty-four of the 48 patients treated in this manner had successful resolution of their problem. Four patients were found to have primary Crohn's disease of the colon and required further treatments in addition to closure of the fistula.