We herein present the findings of a 10-year-old boy with non-Hodgkin's lymphoma of the ascending colon which caused intussusception and intestinal bleeding. He had a history of Becker muscular dystrophy. However, he had neither hypertrophic calves nor cardiomyopathy, and his serum creatine kinase (CK) level always exceeded 2000 IU/l. Preoperatively, a laboratory examination revealed high serum levels of CK (2038IU/l), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH), and the blood hemoglobin level was 7.0g/dl. A barium enema examination revealed an intussusception in his ascending colon, which was found to be a highly vascular tumor on Doppler ultrasound scans. A right hemicolectomy was performed. Macroscopically, the 5 x 6 x 8-cm solid tumor of the ascending colon resembled a submucosal tumor and had two ulcerous lesions at the tip. The tumor was histologically diagnosed to be a diffuse large B-cell lymphoma of the ascending colon. General examinations revealed no involvement of lymphoma postoperatively. At 13 months after surgery, the CK (37861U/l), AST (110lU/l), ALT (1381U/ l), and LDH (420lU/l) levels are still high, and the patient is doing well without any signs of recurrence.