There are sparse epidemiologic data on coinfection of hepatitis B (HBV) and hepatitis C (HCV) in the United States. Therefore, the aim of this study was to determine the prevalence and predictors of HBV coinfection in a large U.S. population of HCV patients. We used the National Veterans Affairs HCV Clinical Case Registry to identify patients tested for HCV during 1997-2005. Patients were categorized based on HCV exposure (any two +HCV tests or one test with a diagnostic code), HCV infection (+RNA or genotype), HBV exposure (any +HBV test, excluding +HBsAb only), and HBV infection (+HBsAg, HBV DNA, or HBeAg). The prevalence of HBV exposure among patients with HCV exposure and that of HBV infection among patients with HCV infection were determined. Multivariate logistic regression evaluated potential demographic and clinical predictors of HBV coinfection. Among 168,239 patients with HCV exposure, 58,415 patients had HBV exposure for a prevalence of 34.7% (95% confidence interval [CI] 34.5-35.0). Among 102,971 patients with HCV infection, 1,431 patients had HBV coinfection for a prevalence of 1.4% (95% CI 1.3-1.5). Independent associations with HBV coinfection compared with HCV monoinfection were age ≤50 years, male sex, positive HIV status, history of hemophilia, sickle cell anemia or thalassemia, history of blood transfusion, cocaine and other drug use; there was decreased risk in patients of Hispanic ethnicity. Conclusion: This is the largest cohort study in the U.S. on the prevalence of HBV coinfection in HCV patients. Among veterans with HCV, exposure to HBV is common (∼35%), but HBV coinfection is relatively low (1.4%). Several possible risk factors were identified. (Hepatology 2013;58:538–545)