Anteriorly located anus (ALA) is frequently associated with severe constipation accompanied by defecation pain. Between 1988 and 1994, the authors treated 27 children (26 girls, 1 boy; age range, 0 to 11 years) to surgically correct ALA. The operation was performed according to a uniform protocol to longitudinally divide the internal sphincter muscle from the anal skin level to 2 cm above the dentate line on the posterior wall of the anorectum. For anal reconstruction, any of the conventional procedures was employed. Twenty-two of the 27 patients have had follow-up in our clinic for 12 months to 6 years (mean, 2.75 years). Eighteen are completely free of constipation and defecation pain and have regular spontaneous bowel movements. The other four require occasional use of enemas or laxatives. Anal incontinence did not occur in any patient. The results of this study suggest that abnormal function of the internal sphincter is the most likely cause of constipation or defecation pain in patients with ALA and that internal sphincterotomy is the cornerstone of surgical treatment.