Carcinoma of the colon is extremely rare in pediatric patients, and due to the preponderance of poor histological characteristics and the difficulty of diagnosis, the prognosis in children is quite unfavorable. We describe a case of ruptured and disseminated mucinous adenocarcinoma of the descending and sigmoid colon in a 14-year-old boy with abdominal pain, diarrhea and fever. Ultrasonography and computed tomography revealed a large soft tissue mass containing tiny calcifications and poorly enhanced hypodense portions in the thickened descending and sigmoid colon, as well as abundant ascites. Where images reveal a mass with low attenuation, calcifications, and aggressive dissemination, mucinous adenocarcinoma may be preferentially included in the differential diagnosis of a pedriatic colon tumor.