Three types of colitis are now recognized. In the late 1950's and early 1960's, 51 per cent of our patients having colectomy had classic chronic ulcerative colitis. Of our patients operated on at that time, 39 per cent had Crohn's colitis and 10 per cent had colitis of indeterminate type. These three types of colitis should be differentiated because of the high risk of cancer of the colon in patients with long-standing chronic ulcerative colitis. We have not seen an increased risk of carcinoma associated with Crohn's colitis. We performed resection with anastomosis in approximately one third of patients with Crohn's colitis, but recurrent disease developed in two thirds. In contrast, recurrent Crohn's disease developed in only 5.7 per cent of patients having colectomy with ileostomy. Toxic megacolon associated with Crohn's colitis has been seen only in the early clinical stage of the disease. From the standpoint of management and prognosis, attempts to differentiate between the two major types of colitis are appropriate. We have outlined some of the basic clinical and pathologic differences between these two types of colitis.