Infants who are born to hepatitis B surface antigen (HbsAg)-positive women are at high risk for contracting perinatal hepatitis B virus (HBV) infection. When maternal status is known, postexposure prophylaxis (PEP) consisting of a birth dose of (HBV) vaccine and Hepatitis B Immune Globulin may be administered within 12 hr of birth to provide 90% protection. Providers' reporting of maternal HBsAg positivity or perinatal HBV should prompt public health nurses to initiate nurse case management (NCM). NCM is the most successful way to ensure that at-risk infants receive PEP and follow-up serology. Unfortunately, reporting laws vary greatly by state and the Centers for Disease Control and Prevention estimate that perinatal HBV is significantly under-reported nationally. This article discusses public health measures for preventing perinatal HBV and presents a case study that used a novel method to assess the extent of under-reporting. We discuss barriers to public health NCM and the importance of a universal HBV vaccine birth dose to protect undetected and unreported cases. Finally, we suggest implications for public health nursing practice.