According to the various case series, both myelomatous and non-myelomatous paraproteinemias are associated with a second malignant neoplasia in a frequency that ranges between 10 and 22%. This association, with a frequency higher than that statistically expected, is 2 to 4 times higher when compared to the association between two tumors of other origin. The association paraproteinemia-neoplasia was found in 10% of cases of our series of 311 paraproteinemias. In this series epithelial neoplasias are associated with paraproteinemias more frequently than lymphoreticular neoplasias. As far as the Ig class is concerned, there appears to be a prevalence of IgM paraproteinemias, which accounts for 22.5%, while it is only 9% in the general survey of paraproteinemias. The prevalence of the IgM class should be related to the high degree of association (approximately 50%) between the IgM paraproteinemias and lymphoreticular neoplasias. The frequent association with a second neoplasia, common to other malignancies of the B-cell line (chronic lymphocytic leukemia, myeloma), must be considered a greater risk in the prognostic evaluation of a paraproteinemia. This should make us more cautious in affirming the 'benignancy' of every non-myelomatous paraproteinemia.