Monoclonal gammopathy of undeterminated significance (MGUS) and asymptomatic form of myeloma are associated with a long-term risk of progression to active disease symptomatic multiple myeloma or related malignancy. As far as the malignant transformation of MGUS is concerned, size and type of the serum monoclonal immunoglobulin (monoclonal protein, M-protein, M-Ig), serum kappa and lambda free light chain ratio, number of clonal plasma cells in bone marrow, number of clonal plasma cells in peripheral blood, immunophenotype of plasma cells, and another factors seem to play a predictive role.