A study has been made of 93 Japanese patients with Crohn's disease who had not undergone bowel resection at the time of diagnosis during the years 1969 to 1983. Ninety had longitudinal ulcers or a cobblestone appearance or both of the small intestine or colon or both on double contrast barium examination. The incidence of longitudinal ulcers in the small intestine was significantly higher than in the colon (P less than 0.001). Conversely the incidence of cobblestoning was higher in the colon than in the small intestine (P = 0.065). In patients with longitudinal ulceration, there was significantly lower Crohn's disease activity index (CDAI), ESR, and C-reactive protein. Patients with cobblestoning had a significantly higher CDAI, ESR and C-reactive protein, and significantly lower values of albumin, cholesterol in serum, serum iron, haemoglobin, and relative body weight. Our findings indicate that cobblestoning closely correlates with the disease activity of Crohn's disease, and that longitudinal ulceration has a negative correlation. Moreover, our results suggest that the high incidence of cobblestoning and low incidence of longitudinal ulcers in the colon and the reverse in the small intestine reflects the fact that colonic involvement renders the disease more severe than small intestine involvement only.