In 2015, CDC revised the recommendation for the timing of hepatitis B serologic testing for infants born to an HBsAg-positive woman. Postvaccination testing (HBsAg and hepatitis B surface antibody [anti-HBs]) is now recommended 1 to 2 months after completion of at least three doses of the HepB vaccine series, but not before 9 months of age. For a child vaccinated on schedule, testing should be done at age 9 to 12 months. Testing should not be performed before age 9 months because hepatitis B immune globulin (HBIG) might still be present at age 6 to 8 months, nor should testing be performed within 1 month of the most recent HepB dose because a transient false positive HBsAg might occur. Antibody to hepatitis B core (anti-HBc) testing of infants or children is not recommended because passively acquired maternal anti-HBc might be detected up to age 24 months in children of HBV-infected mothers. Children who are HBsAg positive should receive medical evaluation and ongoing follow-up. For additional information, see www.cdc.gov/mmwr/pdf/wk/mm6439.pdf, pages 1118–20.