Hepatitis C virus (HCV) infection is frequent among patients with alcohol use disorders. We aimed to analyse the impact of HCV infection on survival of patients seeking treatment for alcohol use. This was a longitudinal study in a cohort of patients who abused alcohol recruited in two detoxification units. Socio-demographic and alcohol use characteristics, liver function tests for the assessment of alcohol-related liver disease and HCV and HIV infection serologies were obtained at admission. Patients were followed until December 2008; causes of death were ascertained through clinical records and death registry. Cox models were used to analyse predictors of death. A total of 675 patients (79.7% men) were admitted; age at admission was 43.5 years (IQR: 37.9–50.2 years), duration of alcohol abuse was 18 years (IQR: 11–24 years), and median alcohol consumption was 200 g/day (IQR: 120–275 g/day). Distribution of patients according to viral infections was as follows: 75.7% without HCV or HIV infection, 14.7% HCV infection alone and 8.1% HCV/HIV coinfection. Median follow-up was 3.1 years (IQR: 1.5–5.1 years) accounting for 2,345 person-years. At the end of study, 78 patients (11.4%) had died. In the multivariate analysis, age at admission (HR = 1.71, 95%CI: 1.05–2.80), alcohol-related liver disease (HR = 3.55, 95%CI: 1.93–6.53) and HCV/HIV co-infection (HR = 3.86 95%CI: 2.10–7.11) were predictors of death. Younger patients (≤43 years) with HCV infection were more likely to die than those without viral infections (HR = 3.1, 95%CI: 1.3–7.3; P = 0.007). Among patients with alcohol-related liver disease, mortality rate was high, irrespective of viral infections. These data show that HCV infection confers a worse prognosis in patients with alcohol use disorders.