The long-term function of ileoanal pouches is difficult to predict. Whilst many patients have consistently good or bad function, others may experience considerable variation. We have studied pouch function in a prospective consecutive series of patients to determine common patterns and their frequency. In addition several variables have been asessed to see if these can predict long-term pouch function. All 103 patients undergoing ileoanal pouch surgery under the care of one colorectal surgeon have been prospectively studied. Detailed demographic, surgical and outcome data were collected at the time of operation and at subsequent clinic visits over a 10-year period. Pouch function at each visit was assessed using a validated scoring system. Five patterns of pouch function were identified: 1. Consistently good (57%, n = 53), 2. initially bad but improving (18%, n = 17), 3. initially good but worsening (10%, n = 9), 4. consistently bad (8%, n = 7), 5. erratic function with no pattern (8%, n = 7). Ten patients were excluded due to incomplete follow-up data. None of the following variables were found to be predictive of function: age, sex, extent of colitis, duration of disease, single stage of procedure and formation of temporary dysfunctioning loop ileostomy (χ2 = n/s). One quarter of patietns end up with bad or erratic long-term function following ileoanal pouch surgery. The individual characteristics that we studied could not predict this subset.