We report a case of malignant lymphoma arising as a giant perirenal mass in a 62-year-old woman who presented with an enlarging abdominal mass. Computed tomography (CT) revealed a large homogeneous mass with a diameter of 20 cm arising in the retroperitoneum. It surrounded the left kidney without renal infiltration and accompanied with para-aortic lymph node enlargement. Compared with the renal cortex, the tumor showed a homogeneous isodense mass by plain CT and only slight enhancement by the contrast-enhanced CT. On the basis of these imaging studies, the tumor was diagnosed as lymphoma. Then, a US guided percutaneous biopsy was performed and the tumor was diagnosed as malignant B-cell lymphoma by the histopathological analysis. This patient was treated by systemic chemotherapy since tumor cells were also disseminated in the bone marrow. The tumor responded well to the chemotherapy and about 70% of regression was achieved after six courses of chemotherapy.