OBJECTIVES: To examine the geographic, age, gender and racial variations of hepatitis B virus (HBV) infection prevalence in the U.S. Medicaid population.  METHODS: A retrospective study was conducted among the Medicaid fee-for-service (FFS) population in 2008 and 2009. Patients with an HBV diagnosis were identified using International Classification of Disease, Clinical Modification (ICD-9-CM) diagnosis codes 070.22, 070.23, 070.32, 070.33 and V02.61. Two years of continuous Medicaid FFS enrollment were required, and patients with managed care enrollment during the study period were excluded. HBV prevalence was stratified by region, state, age, gender and race. Descriptive statistics were calculated as number and percentage of patients in each category.   RESULTS: A total of 5,944 patients (0.12%) were diagnosed with HBV in 2008 and 2009. For HBV patients age 40-59 years, prevalence was the highest at 0.30%, followed by age group 60+ at 0.08%, and 0-39 at 0.05%. Prevalence stratified by race was examined, and Asian patients had the highest rate at 0.95%, compared to Black (0.17%), Hispanic (0.11%), Native American (0.09%) and White (0.08%) patients.  Male patients were found to have a relative higher prevalence of HBV than female patients in the Medicaid population (0.19% vs. 0.08%). Geographic variation was analyzed, and the highest HBV prevalence was observed in Washington, DC (1.30%), followed by New York (0.35%), Minnesota (0.32%), Alaska (0.25%) and Connecticut (0.24%). The Northeastern U.S. region was found to have the highest prevalence (0.24%), compared to the Midwest (0.10%), South (0.06%) and West (0.06%).  CONCLUSIONS: Middle-aged patients had a higher probability of being infected with HBV than other age groups. Stratified by race, Asian patients were more likely to be diagnosed with HBV. In addition, female patients residing in the Northeast were at higher risk for an HBV diagnosis.