Most lymphomas in the kidney represent secondary renal involvement. Primary renal lymphomas are rare. Lymphomas arising in the urinary tract and male genital organs make up less than 5% of extranodal lymphomas. Kidney is the most common location for GU lymphomas. The image shows a primary renal lymphoma, diffuse large B-cell type, in a 56 y/o male forming a discrete 10 cm mass. The tumor was composed of CD19+, CD20+, and CD10+ B-lymphocytes that were monoclonal for lambda light chains. Immunohistochemical markers for renal cell carcinoma and T-cells were negative. This case is unusual on two counts - 1) this is a primary renal lymphoma which is exceedingly rare, and 2) it is forming a discrete mass simulating renal cell carcinoma instead of diffusely infiltrating the renal parenchyma.