Some studies have suggested that chronic hepatitis C virus (HCV) infection may induce an accelerated decline of forced expiratory volume in 1 second (FEV1). 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 FEV1 (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.