The long-term outcome of Crohn's disease was reviewed in 139 patients who were treated at the Cleveland Clinic for a minimum of 15 years. At the time of diagnosis, 38 (27 percent), 39 (28 percent) and 62 (43 percent) patients had small-bowel, large-bowel, and ileocolic patterns of disease, respectively. The disease progressed with time and, eventually, 104 (75 percent) patients had ileocolic disease. One hundred twenty-two patients (88 percent) underwent at least one definitive operation for the disease. Forty-four (32 percent) patients had proctocolectomies and 65 (47 percent) have ileostomies. Associated manifestations of Crohn's disease occurred in a high proportion of patients; perianal disease in 78 (56 percent), intestinal fistulas in 45 (32 percent), extraintestinal disease in 49 (35 percent). Six patients died of causes directly related to the disease. Specific complications tend to occur at definite times in the course of the disease. Crohn's disease is not a benign condition. There is a relentless progression of the disease and a high incidence of complications when patients are followed over a long period.