Strength of association between hepatitis C virus and different diseases in the context of hepatitis C virus syndrome. The spectrum of different hepatitis C virus (HCV)-associated immunological and neoplastic disorders may be classified on the basis of clinico-epidemiological, histopathological, and molecular biology studies in three different levels. High: the association with HCV infection characterizes the large majority of patients; HCV infection is one of the major triggering agents of the disease. Medium: patients with the disease show a significantly higher prevalence of HCV infection compared to controls; the putative pathogenetic role of HCV is also supported by pathogenetic studies and it may identify at least a specific disease subset. Low: the possible association is suggested by limited clinico-epidemiological observations; a pathogenetic link in at least a specific disease subset from some geographical areas is probable, but needs to be definitely demonstrated. Other possible associations have been suggested (see text) on the basis of anecdotal observations. B-cell NHL, B-cell non-Hodgkin's lymphoma; HCC, hepatocellular carcinoma.