Abstract： Objective To introduce a common but not well-recognized acute abdominal disease in children.Methods Thirty-eight children with spasm of the internal anal sphincter were reviewed. Results The main symptom was the sudden onset of continuous pain in the lower abdomen with paroxysmal exacerbation. The typical sign was the dilation of the sigmoid colon with tenderness aggravated by pressure. Plain X-ray films showed dilation of the sigmoid colon and rectum. The symptoms could be relieved by digital rectal examination or a glycerin suppository.Conclusions It is the temporary achalasia of the internal anal sphincter that causes acute abdominal pain.