Anorectal function and colonic transit was assessed in 17 severely constipated patients and 15 age-matched controls. The constipated patients were divided into those who had "immobile perineum" (perineal descent < or = 1.0 cm during attempted defecation) and those who had a normal descent (> 1.0 cm) of the perineum. When constipation was accompanied by an immobile perineum, patients had impaired balloon expulsion, impaired and delayed artificial stool expulsion, decreased straightening of the anorectal angle, decreased descent of the pelvic floor with defecation, and prolonged rectosigmoid colon transit compared with the patients with constipation who had a mobile perineum and with normal controls. The mobile-perineum group differed from controls only in colon transit times, having prolonged total colon transit. Anal sphincter resting pressures, immediate artificial stool expulsion, resting anorectal angles, and electromyography of the external anal sphincter and puborectalis did not differentiate the constipated patients from the controls. We concluded that descent of the perineum of < 1 cm was associated with impaired expulsion, an adynamic anorectal angle, and slowed distal colon transit. This simple sign of pelvic floor function distinguished constipated patients with disordered expulsion from constipated patients with normal pelvic floor function. These patients may respond poorly to surgery and conventional management and would therefore be candidates instead for pelvic floor retraining. Accurate characterization and appreciation of pelvic floor dysfunction in patients with severe chronic constipation may improve the selection for and results of surgical and nonsurgical intervention.