Sixty-seven patients with a J-shaped ileonanal pouch were studied over a 2-year period with regular recording of sphincter and pouch characteristics and analysis of their role in functional outcome. Although there was a 27 per cent permanent reduction in resting anal pressure (RAP) (P less than 0.001), two-thirds of the patients still had a RAP within the normal range. The mean(s.d.) pouch volume increased during the first year from 132(46) ml to 282(85) ml. RAP was not related to functional outcome and preoperative RAP was not predictive of subsequent function. Large pouch volume and compliance correlated with low defaecation frequency (range of r = 0.27-0.36; P less than 0.05) and good overall function (r = 0.37-0.56; P less than 0.01). The initial pouch volume was predictive of subsequent overall function. The ileal length used for pouch construction predicted subsequent pouch volume (r = 0.48; P less than 0.001) and to some extent functional outcome (r = 0.28-0.37; P less than 0.05). However, the studied variables accounted for only 21 per cent of the total variance of functional outcome.