Data for 500 patients with Crohn's disease who underwent operations were analyzed (316 patients, 1966 to 1969; 184 patients, 1972 to 1973) by comparison of various anatomic disease locations (clinical pattern): (1) ileocolic, 225 patients; (2) small intestinal, 130 patients; (3) colonic, 127 patients; (4) anorectal, 18 patients. Indications for surgery were tabulated and compared using statistical analysis for the three large patterns. For patients with ileocolic Crohn's disease, the primary surgical indications were internal fistula and abscess, 44%, intestinal obstruction, 35%, and perianal disease, 12%. For patients with Crohn's disease of the small intestine, the primary surgical indications were intestinal obstruction, 55%, and intestinal fistula and abscess, 32%. Patients with colonic Crohn's disease had a significantly more diverse surgical indication, with poor response to medical therapy, 26%, internal fistula and abscess, 23%, toxic megacolon, 20%, and perianal disease, 19%. These values were highly statistically significant (P less than 0.0001) in all instances but one. This study demonstrates that statistically significant differences occur in the surgical indication depending on the location of Crohn's disease. Patients with ileocolic, small intestinal, and colonic involvement have striking differences in clinical course. It is concluded that Crohn's disease is not a homogeneous entity, but should be recognized as having a varying course depending on clinical pattern.