Although cases of lichen planus (LP) associated with hepatitis C virus (HCV) infection have been described, the association between the two diseases has not been established because the geographic origin of patients could be an important factor in HCV prevalence in patients with LP. The serum samples of 78 consecutive patients with cutaneous and/or mucous LP and 82 control patients were analysed for the presence of antibodies to HCV by enzyme-immunoassay and for the presence of antigens of HCV by two-stage polymerase chain reaction (PCR). The clinical features of patients with LP associated with HCV infection were compared with patients with LP without HCV infection. Sixteen of the 78 (20%) patients had anti-HCV antibodies. In 13 of these 16 cases (81%), HCV-RNA was detected by PCR in serum samples. In the 82 control patients, anti-HCV antibodies was observed in two (2.4%) patients. We have found a statistically significant association (P < 0.05) between erosive LP and HCV infection. We conclude that the high prevalence of HCV-RNA in patients with LP provides some evidence for the role of HCV in the pathogenesis of LP. Our results suggest an association between erosive LP and HCV infection.