OBJECTIVE To evaluate the long-term functional outcome of colonic J-pouch reconstruction after low anterior resection (LAR) for rectal cancer in a prospective study. METHODS We compared the functional outcome of 46 patients who underwent J-pouch reconstruction (J-group) and 49 patients who underwent straight anastomosis (S-group) after LAR for rectal cancer. We evaluated clinical function using a 17-item questionnaire about different aspects of bowel function. Physiologic reservoir function was evaluated by manovolumetry. RESULTS Among the patients with an ultralow anastomosis (<or=4 cm from the anal verge), those in the J-group had fewer bowel movements during the day and at night, and less urgency, soiling, protective pad use, incontinence, and dissatisfaction with bowel function than those in the S-group. Among the patients with a low anastomosis (5-8 cm from the verge), those in the J-group had fewer bowel movements at night, and less urgency and soiling than those in the S-group. Moreover, reservoir function (reflected by the maximum tolerable volume, threshold volume, and compliance) was better in the J-group than in the S-group in both the ultralow and low anastomosis groups. CONCLUSIONS J-pouch reconstruction after low anterior resection creates a better stool reservoir than straight anastomosis, especially when the anastomosis is less than 4 cm from the anal verge, resulting in a better quality of life 3 years after rectal cancer resection.