A 15-year-old boy who had not defecated for 1 week was diagnosed as having a mucinous adenocarcinoma in the descending colon. Microscopically, the outermost layer of the colon and the omentum showed metastatic mucinous-type adenocarcinoma. Adenocarcinoma of the colon is an unusual disease in patients under 30 years, and generally presents as advanced disease. No other abnormal laboratory results were found before surgery. Colon cancer should not be excluded in childen only on the basis of age. Clinical characteristics, diagnosis, and treatment of colon cancer in pediatrics are discussed.