OBJECTIVE Colonic J-pouch anastomosis after low anterior resection of the rectum has been reported to be associated with an increased risk of evacuation difficulty. Using scintigraphy we compared neorectal emptying after stapled low anterior resection between colonic J-pouch anastomosis and straight anastomosis. METHODS We studied 19 patients after colonic J-pouch anastomosis and 22 after straight anastomosis. After the introduction of an artificial stool containing (99m)Tc-DTPA into the neorectum sequential lateral gamma images were obtained. From the time activity curve of radioactivity in the whole pelvis the time taken to evacuate one-half of the introduced artificial stool ( t(1/2)) and the percentage of artificial stool evacuated in 1 min (Evac(1)) were calculated. Fourteen volunteers were also studied as the reference group. RESULTS The t(1/2) was significantly longer and Evac(1) significantly lower in patients after low anterior resection than in the reference group. t(1/2) was significantly longer in the pouch group than in the straight group. Anastomotic height was significantly correlated with both t(1/2) and Evac(1). Neither t(1/2) nor Evac(1) was correlated with the severity of impaired defecatory function. CONCLUSIONS Although neither of the two parameters of neorectal emptying was correlated with the severity of impaired defecatory function, less effective neorectal emptying in patients after colonic J-pouch anastomosis than in those after straight anastomosis may be a factor causing evacuation difficulty after colonic J-pouch anastomosis.