Colorectal carcinoma, primarily a disease of adulthood, accounts for 0.2% of malignancies in adolescents and has very rarely been reported in childhood. Herein, we report a 15-year-old boy who presented with rectal bleeding, lower abdominal pain, and diarrhea. His physical examination revealed tender abdomen with hepatomegaly. A hard mass was palpated by digital rectal examination. Histologic examination revealed a mucinous rectal adenocarcinoma. He died 4 months after diagnosis. This case highlights the need for awareness of colorectal carcinomas and their invasive nature in the differential diagnosis of rectal bleeding and diarrhea in adolescents.