A pathogenetic role of HCV has been recently postulated in some lymphoproliferative disorders and in particular in essential mixed cryoglobulinemia. To assess the relevance of HCV infection in multiple myeloma, Waldenström's macroglobulinemia and monoclonal gammopathy of undetermined significance in the absence of cryoglobulinemia (cryo-ve MG), 102 patients were evaluated for antiHCV, HCVRNA and HCV genotypes. A control group of 466 patients referring for acute trauma to the Orthopedic Division of our hospital was also studied. The overall prevalence of HCV was 15.6% in MG patients and 5.4% in the control group (P= < 0.001). Since only patients with MG older than 50 years had HCV infection, we compared the prevalence rate of infection in patients aged 50 and older: in cryo-ve MG HCV prevalence was 17.9%, while in patients with an acute trauma it was 10%; the difference was not statistically significant. In addition, occurrence of cryo-ve MG was investigated in 614 antiHCV+ patients with chronic liver disease and was found in 1.9%. Comparing all the 28 cryo-ve MG patients HCV+ with an appropriately matched control group of HCV+ patients without MG, no difference in severity of liver disease and genotype distribution was detected. These findings show that: (1) among cryo-ve MG, HCV infection is frequent as shown in the appropriately matched control population; (2) prevalence of cryo-ve MG in antiHCV patients with chronic liver disease is similar to the rate found in the general population; and (3) HCV infection and disease do not differ in patients with and without cryo-ve MG.