In 12 patients with constipation, it was detected by defecography that, during straining, the anorectal angle did not increase, but remained at 90 degrees. These patients were unable to excrete barium. Since the anorectal angle is a measure of activity of the pelvic floor musculature, a dysfunction of this muscle was suspected. In order to determine whether this abnormality represented a true functional disorder or just a voluntary contraction of the pelvic floor muscles due to embarrassment, we performed electromyographic, manometric, and transit time studies in these patients. The electromyographic studies confirmed the persistent contraction during defecation straining. Both manometry and electromyography revealed normal muscle function at rest and during squeezing. Colonic transit time studies demonstrated rectal retention in nine of 12 patients, indicating outlet obstruction. Persistent contraction of the pelvic floor muscles, for which we propose the name "spastic pelvic floor syndrome," represents a functional disorder of normal pelvic floor muscles, causing a functional outlet obstruction.