Mass vaccination of all newborns against hepatitis B virus infection has been implemented in Malaysia since January 1989. The significance of perinatal transmission of hepatitis B virus and the prevention of the disease are discussed. Routine screening of 6443 mothers in the University Hospital showed an overall carrier rate of 1.9%; whilst this was high amongst the Chinese (4.7%), a significant number of Malays were also infected (1.6%). The mechanism of perinatal transmission of hepatitis B and the important role of routine screening of antenatal mothers in eradicating the disease are discussed.