Some studies have suggested that chronic hepatitis C virus (HCV) infection may induce an accelerated decline of forced expiratory volume in 1 second (FEV(1)). We performed a cross-sectional study to determine the prevalence of HCV infection in a sample of chronic obstructive pulmonary disease (COPD) patients and in a control group of blood donors. The clinical characteristics of HCV-positive and HCV-negative patients were compared. Anti-HCV antibody was determined and confirmed by HCV-RNA. The prevalence of HCV infection in COPD patients was 7.5% (95% CI 6.52-8.48) and in blood donors was 0.41% (95% CI 0.40-0.42). The HCV-positive patients had a lower FEV(1) (34.7 +/- 8.6%) and a higher BODE index (median = 6) than HCV-negative patients (42.7 +/- 16.5%, median = 4, respectively) (P = 0.011 and 0.027, respectively). Our results suggest a high prevalence of chronic HCV infection in patients with COPD in comparison with the blood donors. HCV-positive patients have a more severe disease.