Hepatitis C virus (HCV), a hepatotropic and lymphotropic virus, is the major causative agent of nonA-nonB chronic hepatitis; moreover, it is frequently associated with benign and malignant lymphoproliferative disorders such as mixed cryoglobulinaemia and B-cell non-Hodgkin's lymphoma (NHL). We investigated the clinical and virological features of B-cell NHL complicating chronic hepatitis C in a series of 10 patients (M/F 1/9; mean age 63 +/- 6SD years). The malignancy appeared after median 8 +/- 4SD years from onset and was low-grade in six patients, intermediate in three, and high-grade in one. 'One-tube nested' PCR detected serum HCV RNA and viral ongoing replication in both fresh and cultured peripheral lymphocytes in all ten. Analysis of HCV genotypes showed a relatively higher prevalence of 2a/III type compared with unselected chronic hepatitis C (50% vs. 15%). In one patient, HCV RNA was also found in the neoplastic bone marrow and lymph-node specimens. B-cell NHL can complicate chronic hepatitis C and affect the overall prognosis of the disease. The increasing frequency of chronic hepatitis C worldwide suggests that the actual prevalence of this complication may be underestimated. Careful clinical work-up at diagnosis and during follow-up is particularly recommendable.