Treatment of chronic hepatitis C infection (HCV+) has historically been shown to be less effective in patients with a heavy drinking history. The effect of moderate and heavy alcohol use on treatment with pegylated interferon-alpha and ribavirin (P/R) in an insured household population has not been previously reported. We investigated the effect of alcohol on treatment outcome in a cohort of 421 treatment-naïve HCV+ patients, members of an integrated health care plan treated with P/R between January 2002 and June 2008. A detailed drinking history was obtained for 259 (61.5%) eligible patients. Regular drinking was reported by 93.1% of patients before HCV diagnosis, by 30.9% between HCV diagnosis and treatment, by 1.9% during treatment, and 11.6% after the end of treatment. Heavy drinking patterns were reported by 67.9%, 63.5% of patients drank more than 100 kg of ethanol before initiating HCV treatment, and 29.3% reported abstaining less than the required 6 months before treatment. Despite these reports of heavy drinking, sustained virological responses (SVRs) were obtained in 80.2% of patients with HCV genotypes 2 or 3 and 45.1% of patients with genotypes 1, 4, or 6. Pretreatment drinking patterns and total alcohol intake were both unrelated to SVR rates. Abstaining less than 6 months before treatment was related to lower SVR rates in moderate, but not heavy, drinkers. HCV treatment relapse was unrelated to drinking after treatment ended. Conclusion: The amount of alcohol consumed before HCV treatment did not have a negative effect on treatment outcomes in our population. A history of heavy drinking should not be considered a deterrent to HCV treatment in members of an integrated health care plan who are closely monitored. (HEPATOLOGY 2012)