PURPOSE:Different studies have shown that low colorectal and coloanal anastomosis often yield poor functional results. The aim of the present study was to investigate whether a colonic reservoir is able to improve functional results.METHODS:Thirty‐eight consecutive patients subjected to low anterior resection were randomized following rectal excision in two groups. One (n=19) had a stapled straight coloanal anastomosis, and the other (n=19) had a 10‐cm stapled colonic pouch low rectal anastomosis. Median anastomotic distance above the anal verge was 3.38±0.56 cm and 2.14±0.36 cm in both groups, respectively. Continence alterations, urgency, tenesmus, defecatory frequency, anal resting and maximum voluntary squeezing pressures, and maximum tolerable volume were evaluated one year later.RESULTS:One patient died of pulmonary embolism, and seven presented with a recurrence and were excluded from the study. Stool frequency was greater than three movements per day in 33.3 percent of cases with a reservoir and in 73.3 percent of those with a straight coloanal anastomosis(P<0.05). Maximum tolerable volume was significantly greater in patients with a reservoir (335 ± 195) than in those without (148 ± 38)(P<0.05). There were no significant differences in other variables studied.CONCLUSIONS:This study shows that some aspects of defecatory function after rectal excision could improve with a colonic reservoir.