Primary manifestation of malignant lymphoma and/or leukaemia rarely occurs in the kidney. It can be the cause of a hitherto unexplained acute renal failure or it is incidentally detected as shown in the three cases under report.1.A 68-year-old man was operated on because of a symptomatic tumour in his right kidney. At nephrectomy, a conventional (clear cell) renal cell carcinoma was found simultaneously with an occult mantle cell lymphoma infiltrating the adjacent renal and extrarenal tissue. Clinical follow-up uncovered nodal and bone marrow involvement, so that a primary renal manifestation of mantle cell lymphoma was apparent.2.A 69-year-old man with suspected vertebral metastasis underwent partial renal resection because of a mass in his left kidney. Histologically and immunohistochemically, the renal infiltration was diagnosed as a precursor B-lymphoblastic lymphoma. After chemotherapy and irradiation, leukaemic blood cell counts with 50% lymphoblasts proved a primary renal manifestation of precursor B-lymphoblastic leukaemia/lymphoma.3.A 13-year-old boy presented clinically with renal failure, enlarged kidneys, and normal urinalysis. Renal biopsy showed a diffuse interstitial infiltration with atypical T-lymphoblasts compressing tubules and surrounding preserved glomeruli. Subsequent clinical bone marrow smears presented 60% T-lymphoblasts, so that the final diagnosis of a primary renal manifestation of acute T-lymphoblastic leukaemia of mature thymic cortex type was made. Immediate chemotherapy resulted in total recovery of renal function and bone marrow findings.