Changing patterns of the lesions in colonic Crohn's disease were studied in 86 patients who underwent multiple consequetive roentgen examinations. Local progression of lesions was seen in 56 out of 86 patients; rapid local advancement from mild to severe lesions was not uncommon. Temporary regression of lesions was only seen in 7%; definitive permanent healing on conservative treatment was not observed. Preoperative extension of lesions was seen in 29%, with ultimate involvement of the rectum in 7% and development of anal fistulae in 17%. Clinical implications of the findings are briefly discussed.