A rare adult case of intussusception caused by malignant lymphoma of the cecum with intramural metastasis is reported. The patient was a 24-year-old man. Ileocolic intussusception was diagnosed by characteristic findings on abdominal computed tomography. Endoscopic examination revealed a massive protuberant tumor, 3 cm in diameter, and a semipedunculated polyp, 1 cm in diameter, in the cecum, which had caused the ileocolic intussusception. Endoscopic biopsy specimens failed to yield a definitive diagnosis histologically, but right hemicolectomy with lymph node dissection was performed. On histologic examination of the surgical specimens, both the tumor and the polyp were diagnosed as diffuse lymphoma of medium-sized cell type, and no lymph node involvement was found. The patient responded well to surgical and chemotherapeutic treatment, and has had no recurrence of malignant lymphoma in the 2 years since the surgical treatment. This was a very rare case of an intussusception in an adult patient due to malignant lymphoma in the cecum with intramural metastasis and without lymph node involvement.