PURPOSE:Improved functional results can be obtained by construction of a colonic J‐pouch after coloanal anastomosis. Variability in pouch size following coloanal anastomosis is prevalent in current literature. In this study, the authors compare clinical bowel function after complete rectal excision with coloanal anastomosis for patients with rectal carcinoma using either a small 6‐cm or a large 10‐cm colonic J‐pouch anastomosis. The clinical outcome is assessed both at short‐term and long‐term follow‐up.METHODS:Fifty‐nine consecutive patients with rectal cancers 4 to 8 cm from the anal verge were recruited into the study. Patients were randomized intraoperatively to either a 6‐cm J‐pouch group or a 10‐cm J‐pouch group. Clinical assessments were performed prospectively at 3, 6, 12, and 24 months postoperatively, following colostomy closure. Clinical parameters such as frequency, urgency, continence, and laxative and enema use were assessed and compared between the two groups.RESULTS:There was no statistical differences in the mean defecation frequency, urgency, and fecal continence between the two groups at 3, 6, 12, and 24 months. In the first year, laxative and enema use between the two groups was negligible; however at two years, 30 percent of patients with a large reservoir compared with 10 percent of patients in the small‐pouch group required laxative and/or enema for constipation and evacuation of bowels.CONCLUSION:Similar clinical results can be expected from patients with either small or large reservoirs at one year. However, with long‐term follow‐up, patients with a large reservoir are more likely to require medication for constipation and evacuation. To avoid these inconveniences a small reservoir is advocated for patients undergoing coloanal anastomosis.