Proteinuria is frequently found in multiple myeloma and related disorders. Immunofixation electrophoresis is very helpful for the identification and characterization of the monoclonal component. In multiple myeloma, the presence of Bence-Jones (BJ) proteinuria is significantly associated with renal failure. The coexistence of BJ proteinuria and the nephrotic syndrome in myeloma patients should suggest AL amyloidosis or light chain deposition disease. In the latter, BJ proteinuria is absent in 30% of the cases and diagnosis is based on the demonstration of the monoclonal light chain deposits in tissues, predominantly in kidneys.