OBJECTIVE Since selective screening for Hepatitis B virus (HBV) in pregnant women has failed to identify a high proportion of HBV-infected mothers, pre-natal HBsAg testing of all pregnant women is now recommended. We aimed to determine the prevalence of HBV infection among pregnant women at the ante-natal clinic of a tertiary care center in Saudi Arabia and to identify the target group for postpartum immunization. METHODS A total of 755 pregnant females who attended the antenatal clinic from June 2005 to June 2006 for the first time - before 38 weeks of gestation - constituted the target of the present study. Blood samples 30-39 were drawn from all subjects and sera were tested for HBV serologic markers including Hepatitis B surface antigen, anti-HBs, and anti-HBc using ELISA technique (third generation). RESULTS The overall prevalence of sero-positive HBsAg among pregnant women was 1.6%. As age increased, the prevalence of sero-positive HBsAg significantly increased (chi(2) = 116.43, P < 0.001), 30-39 were women aged >or=40 were five times more likely to be positive for HBsAg as compared to those <30 years (OR = 4.78). On the other hand, women aged 40 and over were five times more likely to be susceptible to infection with hepatitis as compared to young women aged <20 (OR = 5.15). Women susceptible to HBV infection constituted about 80% of all pregnant females. CONCLUSIONS These findings reflect that the full impact of the Hepatitis B vaccination program that was conducted in 1989 for all Saudi children has not yet reached all pregnant women, with the majority (79.9%) being nonimmune and thus liable to HBV infection. Postpartum HB immunization should be recommended in such cases.