Sexual transmission accounts for the majority of hepatitis B virus (HBV) infections in industrialized countries. Hepatitis A virus (HAV) can be transmitted by sexual practices that involve fecal-oral exposure. Both infections are disproportionately frequent in men who have sex with men (MSM). Routine immunization against HBV is recommended for MSM and for persons being evaluated or treated for sexually transmitted diseases (STDs), and HAV immunization is advised for MSM and for other persons at risk who are commonly seen in STD care settings, such as users of illegal drugs. However, numerous attitudinal and structural barriers interfere with routine immunization in persons at risk for sexual acquisition of HAV and HBV. Substantial success has been documented in vaccinating persons at risk in public STD clinics and other settings; however, at a national level, efforts to achieve desired immunization rates have largely failed. Until universal childhood immunization produces a largely immune adult population, the universal vaccination of adults-as a supplement to the current risk-based approaches-may be worthwhile to achieve immunization of persons at risk for sexual transmission of HBV.