Anorectal myectomy was performed in 62 patients suffering from symptoms attributed to ineffective colonic motility. Indications for surgery rested on the presence of one or more of the following three criteria: abnormally reduced stool frequency, prolonged transit of radioopaque markers, and abnormal anorectal manometry. One year after myectomy in the 50 patients with less than three stools per week the average number of stools per week increased from 1.2 to 4.2 (P less than 0.001). The remaining 12 patients, who had more than three stools per week, were completely relieved of their symptoms. In all cases with improved symptoms, myectomy acclerated the transit of radioopaque markers through the large bowel. Organic constipation amenable to surgical treatment is more frequent than previously thought. Idiopathic constipation may result from colonic inertia or outlet (anorectal) obstruction.