A large serosurvey was carried out in Luxembourg in 2000–2001, to determine the population immunity against a number of vaccine-preventable infections including diphtheria and pertussis. Immunity to diphtheria and pertussis was assessed using an in-house neutralization assay and a commercial ELISA test respectively. Mean pertussis antibody activity decreased from 4 to 8 years of age, reflecting the effects of waning of vaccine-induced immunity. Mean pertussis antibody activity increased during adolescence due to infection in previously vaccinated individuals and levelled out after approximately 20 years of age. For adults >25 years age, a statistically significant 30% difference in mean antibody activity between men and women was observed. The proportion of seronegatives for diphtheria among children and adolescents aged <20 years was 2·5% reflecting the high vaccination coverage. The proportion seronegative for diphtheria tended to increase with age such that 42% of individuals aged >40 years were seronegative. Our study supports the recently introduced acellular pertussis vaccine booster at 6 years to reduce pertussis transmission in school-aged children and adolescents.