Hepatitis C virus (HCV) is a RNA virus that cannot be integrated with the host genome; it can, however, exert its oncogenetic potential indirectly by contributing to the modulator effects of the host immune system, probably through a capacity to elude the immune system. We have carried out a case controlled study on tumors correlated with the immune system (multiple myeloma, non-Hodgkin lymphoma and Hodgkin disease) and HCV, in a high prevalence area. The relationship between each cancer and HCV infection was assessed by means of odds ratios (ORs) and corresponding 95% confidence intervals. Risks were greater for B-cell non-Hodgkin lymphoma (OR=3.7, 95%CI, 1.9-7.4, P=0.0001) and multiple myeloma (OR=4.5, 95%CI, 1.9-10.7, P=0.0004). Our study is particularly important for public health, since it shows that during the coming years in the South of Italy, because of the high prevalence of HCV, there are good reasons to expect not only an increase of liver cancer, but also an increased incidence of great number of tumors correlated with the immune system.