The acute renal failure is characterized by a rapid detoriation of the renal function. In addition to the usual prerenal, intrinsic and postrenal causes of an acute renal failure distinct causes have to be considered for oncological patients. Factors immanent to the malignant disease, e. g. paraneoplastic syndromes or retroperitoneal bulks can account for an acute renal failure. Paraproteins as produced by a multiple myeloma are other possible causes for renal dysfunction. For some anticancer drugs nephrotoxicity is a potential side effect, in particular for cisplatin, methotrexate, ifosfamide and melphalan. A hemolytic uremic syndrome may be induced by mitomycin and gemcitabine. Extensive surgery can be associated with rhabdonnyolysis and myoglobin-uria and results in renal impairment. Treatment of a chemosensitive neoplasia with a highly effective regimen may result in a tumor lysis syndrome with hyperuricemia, hyperkalemia, hyperphosphatemia and hypocalcemia.