The computed tomographic scans of 200 consecutive patients with Crohn disease were studied to determine the frequency and patterns of perirectal and perianal involvement. In 163 patients (82%) abnormalities in the perirectal-perianal region were demonstrated; findings included inflammation of fat planes (73%), bowel wall thickening (30%), fistulas or sinus tracts (22%), and abscesses (14%). Fistulas or sinus tracts occurred with equal frequency above or below the level of the anterior symphysis pubis. Abscesses, rectal thickening, and inflammatory infiltration of fat occurred more than twice as often above the symphysis pubis. However, 37% of patients had manifestations of Crohn disease below the symphysis pubis, emphasizing the importance of extending scanning sequences to the perineum.