The width of the presacral space was measured prospectively at various levels in 100 persons without organic colonic or rectal disease who had barium enema X-ray examinations. A standard technique was employed. The most consistent measurement was obtained at the level opposite the S3-S4 disc space; readings varied between 2 mm and 16 mm. Using 16 mm as the upper limit of normal, and a similar technique of barium enema examination, the width of the presacral space at the S3-S4 disc level was measured in 66 patients with inflammatory bowel disease (ulcerative colitis–49; Crohn's colitis–17). The width did not correlate with the severity of the disease process as indicated by sigmoidoscopic examination in proximity in time to the radiological examination. There was a relationship between increased width of the presacral space and the duration of the disease process.