Numerous studies have documented the efficacy and safety of plasma-derived and recombinant hepatitis B vaccines. However, little is known about the long-term protection of hepatitis B vaccine, when anti-HBs declines to low or undetectable levels. This study reports results from a 9-12-year period follow up of infants immunized against hepatitis B in Senegal. At the end of the follow-up period anti-HBs were detected in 81% of children who received a booster dose at school age and in 68% of those who did not. HBsAg was detected in 19% of infants from the control group compared to only 2% of immunized infants, corresponding to a protective efficacy of 88%. The results show that long-term protection against HBsAg carriage of hepatitis B vaccination is very high and that a booster dose at school age does not significantly increase this protection.