Objective: To evaluate the relationship between hepatitis C viral infection and alcoholic liver disease. Design: Case-comparison study. Setting: Bronx (NY) Veterans Affairs Medical Center. Participants: Forty-seven consecutive alcoholic patients undergoing diagnostic liver biopsy. Main Outcome Measures: Serum was obtained at the time of liver biopsy and assayed for antibodies to hepatitis C virus using enzyme-linked immunosorbent assay, recombinant immunoblot assay, and hepatitis C virus neutralization methods. Results: Antibody to hepatitis C virus, as confirmed by the recombinant immunoblot assay, was strongly associated with the presence of portal and/or lobular inflammation (91% seropositivity) but was only present in 16% of patients without this histologic finding (P<.001). In patients without portal or lobular hepatitis, recombinant immunoblot assay seropositivity was seen in 27% of patients with cirrhosis and 20% of patients with alcoholic hepatitis and was absent in patients with steatosis and/or perivenular fibrosis. In the subgroup of alcoholic patients who were without known risk factors for hepatitis C virus infection (ie, no history of intravenous drug use or blood transfusions), antibody to hepatitis C virus was present in 78% of subjects with portal and/or lobular hepatitis but was absent in those with other types of alcoholic liver disease. Finally, anti-hepatitis C virus-seropositive patients had a significantly greater mean necroinflammatory score as compared with anti-hepatitis C virus-seronegative alcoholic patients (2.1 vs 1.2; P<.001). In contrast, there was no significant difference in the mean fibrosis score between the two groups. Conclusions: The presence of portal and/or lobular inflammation is strongly associated with antibodies to hepatitis C virus in alcoholic patients, even in the absence of known risk factors. This association indicates that hepatitis C virus is responsible, at least in part, for the portal and/or lobular hepatitis associated with alcoholic liver disease.