We have studied 20 patients with the descending perineum syndrome, half of whom were incontinent of faeces. Objective criteria were established in 103 control subjects for determining the relationship of the perineum to the bony pelvis. The anal reflex latency was increased in the 10 patients in whom perineal descent was associated with faecal incontinence, but not in the 10 without incontinence. However, there was hypertrophy of the muscle fibers in external anal sphincter muscle biopsies in all the patients. Thus, abnormal degrees of perineal descent are associated with changes in the external anal sphincter muscle, consistent with damage to its nerve supply.