Neuropathic faecal incontinence is associated with low anal pressures and shortening of the anal canal. The operation of postanal repair has been shown to result in the return of acceptable continence in over 80 per cent of such patients. This paper examines the effect of the operation on anal canal pressures. Forty-two patients with primary faecal incontinence and electrophysiological evidence of neuropathy affecting the external anal sphincter and pelvic floor musculature were studied. Anal pressures were measured before operation and not less than 1 month afterwards. Two groups were chosen according to the clinical result. Group 1 consisted of 34 patients who regained continence and group 2 comprised 8 patients judged as having had an unsatisfactory result. In group 1 there was an increase in anal canal length (1.4 +/- 0.2 cm, mean +/- s.e.m., paired t test, P less than 0.001), resting pressure (19 +/- 3 cm H2O, P less than 0.001) and voluntary contraction pressure (13 +/- 3 cm H2O, P less than 0.001). In group 2 there was some increase in anal canal length (1.0 +/- 0.2 cm P less than 0.01) but no increase in mean resting pressure or mean voluntary contraction pressure. The results show that postanal repair effectively lengthens the anal canal and increases anal pressures in patients with a successful clinical outcome.