Independently of tumor mass or metastases, up to 80% of patients with a variety of neoplastic diseases are exposed to continuous antigenemia (eg, tumor-associated antigens, reexpressed fetal antigens, viral antigens, or autologous antigens of autoimmunity). These antigens stimulate antibody production and form circulating immune complexes and antiideotypic cryoimmunoglobulins. In many instances these immune reactants are deposited or formed in situ in the glomerular mesangium and capillary walls. Multifactorial microhematuria is common among cancer patients; proteinuria without overt NS is found more often in patients with malignancy than in controls and indicates a worse prognosis. Under the proper conditions of host susceptibility and immune deposit nephritogenicity, a few adult cancer patients (< 1%) may develop glomerular injury and overt paraneoplastic renal disease. The glomulopathy, most often MGN, usually is manifested by NS, active urine sediment, and/or diminished glomerular filtration. Significant renal impairment, usually associated with ECGN, is uncommon. In many instances successful treatment of the neoplasm has induced a partial or complete remission of the associated glomerulopathy. The occurrence of overt renal disease in the presence of a malignancy generally augurs a poor prognosis. Whether all patients over the age of 50 with NS caused by MGN should be subjected to especially rigorous cancer surveillance is still an open question, however, prudence, if not cost-consciousness, would seem to favor the affirmative.