Co-infection with HBV and HCV seems to be associated with more severe liver disease in retrospective and cross-sectional studies in adults, but no data are available when co-infection is acquired in youth. The long-term outcome of infection acquired in youth was assessed in patients co-infected with HBV and HCV and in patients with HBV infection only. Twenty-seven patients with HBV and HCV co-infection and 27 patients infected with HBV only were enrolled. Seventy-six per cent of the patients were treated with α-interferon for 1 year. After a median follow-up of 23 years, the annual progression rate of fibrosis was 0.07 in patients co-infected with HBV and HCV, and in those infected with HBV it was 0.07 and 0.11 (P < 0.004) for HBe and anti-HBe-positive patients, respectively. In co-infected patients, the development of cirrhosis was observed in 2 (7.4%) and of hepatocellular carcinoma (HCC) in 1 (3.7%), while in those with HBV, cirrhosis appeared in one patient (3.7%). Alcohol intake (OR = 9.5 ± 1.2; 95% CI = 6.6–13.9; P < 0.0001) was independently associated with cirrhosis and HCC. α-interferon showed no efficacy during treatment, but the treated group showed higher HCV RNA clearance during post-treatment follow-up. Co-infection with HBV and HCV and single HBV infection acquired in youth showed a low rate of progression to liver fibrosis, no liver failure, and low development of HCC during a median follow-up of 23 years (range 17–40). J. Med. Virol. 81:2012–2020, 2009. © 2009 Wiley-Liss, Inc.