Currently many physicians consider enteroenteral fistulas an indication for surgery in Crohn's disease. In an attempt to document the natural history of these fistulas, the courses of 64 patients with Crohn's disease complicated by enteroenteral fistulas were reviewed. The fistulas were diagnosed radiologically in 48 patients (75%) and at operation or by examination of the resected specimen in 16 (25%). Twenty-four of the 48 patients whose fistulas were diagnosed radiologically underwent early operation. The remaining 24 initially had nonoperative management and thus provided information about the natural history of enteroenteral fistulas. Ten of these 24 patients had nonoperative treatment for less than 1 year. All required surgery because of intestinal obstruction, enterovesical fistula, or failed response to medical therapy. Fourteen patients were managed nonoperatively for a mean period of 3.5 years (range 1 to 9 years). Eight of these patients eventually required operation, but the remaining six have to date not needed surgery. In two of these patients the fistulas can no longer be demonstrated radiographically. Patients who initially received nonoperative therapy and later required operation did not have any increased mortality or morbidity as compared with those treated with early surgery. Enteroenteral fistulas are frequently associated with and are the result of active inflammatory disease. The fistulas are usually asymptomatic and are by themselves not considered an indication for operation.