['Positive serum antinuclear antibody (ANA) is present in a number of patients with chronic hepatitis C virus (HCV) infection. This study aimed to evaluate the prevalence of ANA in patients with chronic hepatitis C (CHC) and to elucidate its clinical implications in virological and histological characteristics of CHC infection.', 'A total of 614 CHC patients were enrolled in this prospective, hospital-based study. The serum levels of aspartate aminotransferase, alanine aminotransferase and ANA, and HCV genotype, HCV RNA level, and histological activity index scores for liver histopathology, were determined.', 'The prevalence of positive ANA (titre >1:40) was 35.0%. Women had a significantly higher prevalence than men (41.2 vs 31.0%; p = 0.012). Patients positive for ANA were significantly older (mean (SD), 53.7 (10.5) vs 49.7 (11.3) years; p<0.001) and had higher mean (SD) alanine aminotransferase levels (186.9 (178.8) vs 155.50 (113.5) IU/l; p<0.001) and lower mean (SD) HCV RNA levels (5.2 (0.9) vs 5.4 (1.0) log IU/ml; p = 0.048) than those without ANA. Among 447 patients undergoing liver biopsy, those positive for ANA had a significantly higher mean (SD) fibrosis score (2.0 (1.3) vs 1.5 (1.1); p<0.001) and a higher frequency of F3-4 (69/187, 36.9% vs 50/260, 19.2%; p<0.001) than those negative for ANA. Multivariate logistic regression analyses showed that advanced fibrosis, lower HCV RNA levels and age were significant factors related to positive ANA.'] Is antinuclear antibody associated with a more advanced fibrosis and lower RNA levels of hepatitis C virus in patients with chronic hepatitis C?