Objective. To evaluate the effectiveness of late catch-up vaccination in patients who had not completed their hepatitis B vaccination series. Method. All patients visiting an international vaccination center between September 1999 and March 2010 who were not up to date with their third dose of the hepatitis B vaccine were offered a vaccine dose and, one month later, a follow-up test of their anti-HBs antibody levels. Results. Among the 616 cases retrospectively included in the study, 317 (51.5%) underwent a follow-up serology test. A positive response was observed in 91.5% of them, with a higher immune response rate among women (95.0% versus 88.7%, p=0.04). Overall, the average delay for the third dose was 6.5 years, but it was significantly longer among non-responders (7.7 years). For responders, regardless of the number of years of delay, the antibody titer was significantly higher than 500 IU/L in 73% of cases (p<0.001). A majority of patients (57%) had started vaccination between 1994 and 1998. Conclusion. Despite an average delay of more than 6 years for the third dose, more than 90% of patients who completed their hepatitis B vaccination series and underwent serological testing tested positive for anti-HBs antibodies. Male gender, the delay in vaccination, and age at the start of the vaccination series appear to influence the immune response. The lack of a booster dose seems primarily linked to the controversy that followed the major vaccination campaign of 1994–1998 in France. (R.A.)