Malignant extrarenal rhabdoid tumors are rare. Because they have highly aggressive behavior and exhibit early metastasis, the prognosis is generally poor despite surgical management and chemotherapy. Mortality rates are reported to exceed 80%. This type of malignant tumor preferentially occurs in children aged under 10 years, although they have occurred in adults. We report a case of adult malignant extrarenal rhabdoid tumor of the retroperitoneum which was treated with radical surgery.