The aim of our study was to determine whether ileal pouch motility and evacuability and the 24 hour fecal output influence stool frequency after ileal pouch-anal anastomosis. In 23 patients, at a mean of 24 months postoperatively (range 22 to 26 months), ileal pouch motility was measured using an intraluminal bag and pressure-sensitive catheters. The pattern and efficiency of ileal pouch emptying was determined scintigraphically. A 24 hour stool collection was made and the stool output and stool frequency recorded. The volume of ileal pouch distention at which large amplitude propulsive waves appeared (the threshold volume) correlated closely with stool frequency. The larger the threshold volume, the fewer the stools per 24 hours (correlation coefficient -0.70; p less than 0.01). Also, the greater the 24 hour stool output, the greater the stool frequency (correlation coefficient 0.79, p less than 0.001). In contrast, the efficiency of ileal pouch evacuation was less strongly related to stool frequency (correlation coefficient -0.41, p = 0.05). We conclude that ileal pouch motility and stool output are major determinants of stool frequency after ileal pouch-anal anastomosis. Inefficient pouch emptying is less commonly associated with frequent bowel movements.