The aim of this study was to assess (a) the incidence of perineal descent and (b) the relationship between radiological abnormalities of the pelvic floor and rectoanal manometric disturbances in patients consulting for constipation. Lateral radiographs in both the left lateral and supine positions studied pelvic floor descent. Results obtained in the 25 patients (mean age 47 years) studied were compared with those of 12 controls (mean age 58 years). Pelvic floor descent, never seen in controls, was demonstrated in 14 patients who were older (53 +/- 3 years, mean +/- SD) than the 11 with a normal radiological examination (38 +/- 3 years, p less than 0.05). Anal low pressures (3 cases) and a low amplitude of rectoanal inhibitory reflex (RAIR) (5 cases) were shown only in patients with perineal descent and anal high pressures only in those with normal radiology. Our results suggest that (a) perineal descent is a common finding in over 50% of constipated patients and (b) anorectal motility is related to pelvic floor function.