Obstructed defaecation in the descending perineum syndrome has been attributed to anterior mucosal prolapse. Manometric and radiological measurements together with evacuation proctograms in 49 patients with obstructed defaecation and normal whole gut transit times were carried out and compared in a total of 25 controls. Proctography delineated four groups: (I) puborectalis accentuation, n = 11; (II) rectal intussusception, n = 25; (III) anterior rectal wall prolapse, n = 11; (IV) rectocele, n = 2. The anorectal angle at rest, maximum basal sphincter pressures and the rectoanal inhibitory reflex did not differ between the groups and controls. Group III achieved a greater increase in anorectal angle on straining than controls. Groups II and III exhibited significant perineal descent below the pubococcygeal line whereas group I did not. In perineal descent intussusception was the commonest morphological abnormality associated with obstructed defaecation. Isolated anterior mucosal prolapse was not observed, making local treatment aimed at reducing its bulk questionable.