A 25-year-old man was admitted to our hospital because of hematuria, anemia and thrombocytopenia. Laboratory examinations revealed an increased number of bone marrow megakaryocytes and an increased level of platelet-associated immunoglobulin G, suggesting immune thrombocytopenia. Computed tomography of the abdomen showed enlargement of the bilateral kidneys with multiple low-density areas, although neither lymphadenopathy nor hepatosplenomegaly was evident. After amelioration of the thrombocytopenia by prednisolone therapy, open renal biopsy was performed and a diagnosis of diffuse large B-cell non-Hodgkin's lymphoma was made. The patient achieved complete remission after CHOP therapy. This was thought to be a rare case of primary renal non-Hodgkin's lymphoma initially presenting as immune thrombocytopenia, which was treated successfully by chemotherapy.