Diffuse large B-cell lymphoma involving the kidney in a 70 y/o male. The tumor consists of an intrarenal component as well as a perinephric mass, together measuring about 28 cm in greatest dimension. Immunophenotyping using flow cytometry revealed a population of CD19+ and CD20+ B-cells that were monotypic for lambda immunoglobulin light chains. The patient had previous history of non-Hodgkin lymphoma involving mesenteric lymph nodes. In most cases, the renal involvement is secondary and occurs in the setting of systemic disease. Primary renal lymphomas, however, do occur.