Renal failure in patients with lymphoma or leukemia may be brought about by different causes, including ureteral obstruction, hypercalcemia, hyperuricemia, amyloidosis, immunologically mediated nephrosis and paraproteinemic nephropathy. Lymphomatous or leukemic infiltration of the kidneys is a frequent finding at autopsy but is rarely seen as a cause of renal failure. In this report three patients with lymphomatous infiltration of the kidneys causing renal failure are described. Clinical and laboratory criteria for establishment of diagnosis in such cases are suggested. Using these diagnostic criteria, a renal biopsy may not be necessary.