Oncogenesis is a multifactorial process in which environmental, genetic and infectious factors are variably involved. A possible role of specific viruses has been suggested in at least 15% of human cancers. Hepatitis C virus (HCV), which is both hepato- and lymphotropic, is responsible for various liver disorders, i.e. chronic hepatitis, cirrhosis and hepatocelluar carcinoma, as well as for a constellation of extrahepatic immune-mediated manifestations, among which is mixed cryoglobulinaemia. This is a systemic disorder secondary to a chronic, benign B-lymphocyte proliferation, which in some subjects may evolve to a malignant non-Hodgkin's lymphoma (NHL). Interestingly, recent studies reported the appearance of malignant B-cell neoplasias in patients with type C chronic hepatitis; moreover, in a significant number (from 22% to 50%) of 'idiopathic' NHLs, the presence of HCV infection has been demonstrated. The presence of a geographical etherogeneity in the prevalence of HCV-positive NHL suggests that other co-factors, i.e. genetic and environmental, could be involved in the lymphomagenesis. HCV may exert its oncogenic potential in two different directions, leading to liver cancer or B-cell lymphoma.