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 patients are usually middle-aged or older and there is slight male preponderance. Cases have been reported in children, HIV+ve individuals, and immunosuppressed patients. The presenting symptoms include flank pain, palpable mass, renal insufficiency, and hematuria. Renal lymphomas are bilateral in about 25% of cases. The size ranges from less than 5 cm to massive tumors with complete replacement of renal parenchyma and invasion of adjacent structures such as perinephric fat, psoas muscle, pancreas, or duodenum. Some cases show extension into the renal vein or inferior vena cava. The gross appearance sometimes mimics renal cell carcinoma. The most common type of renal lymphoma is diffuse large B-cell lymphoma (about 40% to 50% of cases). The nephrectomy specimen shown here is from a 65 y/o male who presented with vague abdominal discomfort and weight loss over a 3 year period. There was a soft, pink-tan, bulging tumor infiltrating the calyceal system and extending into the renal vein. On sectioning, this tumor connected with the nodule on the upper left of the image that is extending into the perinephric tissues. The histologic and immunohistochemical profile (POS: CD20, CD22, kappa light chains; NEG: CD2, CD3, & CD5) were diagnostic of diffuse large B-cell lymphoma.