Renal affections are a frequent and clinically important complication of monoclonal gammapathies (MG), in particular of multiple myeloma (MM). The main pathogenetic factor in its development is most probably, despite the participation of other nephrotoxic factors, the action of Bence-Jones protein on the renal parenchyma. Mechanisms of renal affection differ - paraprotein (pp) interferes with tubular functions, precipitates in the cells of the tubular epithelium or in the tubular lumen, is deposited in renal tissue in the form of deposits. The main clinical manifestations include proteinuria, impaired tubular functions and reduced filtration capacity of the kidneys. In 5-10% patients renal failure develops, formerly associated with the unequivocally adverse prognosis of the disease. The change of the therapeutic approach which combines haematological and symptomatic treatment, incl. methods of extracorporeal treatment of the blood, however leads in half the patients to improvement or complete restitution of renal functions. The development of the disease is therefore to a considerable extent determined by the activity of the basic disease and its response to chemotherapy.