Pertussis, a highly contagious respiratory disease, commonly affects infants and young children and can be fatal, especially in babies less than one year of age. Bordetella pertussis continues to circulate even in populations where a high vaccine coverage of infants and children is achieved. Adults are reservoirs for infections in infants, in whom pertussis may be severe and life-threatening. Despite the rising rates of vaccination in our country and all over the world for the past 25 years, the number of pertussis cases among adolescents and adults has been increasing. To decrease the risk of pertussis infection and thus protect adults and adolescents against pertussis, booster doses should be administered to preschool children and adolescents. In order to decide when to administer the booster doses in a country, age-specific seropidemiology of the disease should be known. The aim of this study was to determine the pertussis toxin antibody levels of fully vaccinated healthy children in Isparta, Turkey, aged 10-15 years old. A total of 296 participants, that comprised fully vaccinated 254 healthy elementary-school students aged between 10-15 years (126 male, 128 female) and 42 adults between 18-39 years old (21 male, 21 female) were included in the study with informed consent. The sensitivities of subjects to pertussis were tested by the determination of pertussis toxin IgG levels with the use of commercial ELISA test (Genzyme Virotech, Germany). In our study, the seropositivity rate was found 12.6% (32/254) for 10-15 age group, however all the adult subjects were seronegative. Thus the total seropositivity rate was estimated as 10.8% (32/296). Pertussis toxin IgG seropositivity rate was 12.7% (16/126) for males and 12.5% (16/128) for females, and there was no significant gender difference (p> 0.05). The highest seropositivity rates were detected at 10th (23.8%) and 11th (19%) years in males, and 12th and 14th (23.8%) years in females. No seropositivity was detected in individuals over age 15 in our study. Since adults lose their immune protection gained by pertussis vaccination, they start becoming an infection source for infants. Therefore, a booster dose of acellular pertussis vaccine should be considered in preschool period and at ages 14-18. Further studies regarding diagnosis and surveillance of pertussis disease are required, as well as enhancement of vaccination rates.