The Authors examine the main causes of renal failure in lymphoma (infiltration of kidneys, glomerulonephritis, paraproteinemic nephropathy), the difficulties for a correct diagnosis with ultrasonography, urography and CT scan, the importance of renal biopsy. The histologic examination should be promptly performed in patients with sudden renal failure of unknown aetiology and clinical suspicion of malignancy, because renal function can improve dramatically with aggressive chemotherapeutic treatment of lymphoma.