Asian/Pacific Islanders (A/PIs) in the United States are disproportionately affected by the hepatitis B virus (HBV), which can cause a lifelong liver infection that may result in cirrhosis, liver failure, liver cancer, or death. Although previous studies have measured knowledge of hepatitis B transmission and prevention practices in A/PI communities, we present results from the first population-based study of this type, which specifically focuses on A/PIs who are chronically infected with HBV. Through telephone interviews, we assessed the HBV risk factor knowledge and prevention practices of a population-based, random sample of persons with chronic HBV who were reported to the San Francisco Department of Public Health between October 2007 and July 2009. Among 829 respondents, 67% were foreign born A/PIs of Chinese ethnicity who did not speak English as their primary language. Among all respondents, 75% were unable to identify how they acquired HBV, and 41% said that they do nothing to prevent transmission of HBV to their close contacts. Knowledge of HBV risk factors and recommended prevention practices was poor among A/PIs who are chronically infected with HBV and who may transmit the infection to others.