Adolescents have an unknown true incidence of pertussis and are important reservoirs of transmission. We evaluated the incidence of coughing illnesses, serologic evidence of recent infection and the relationship between symptomatology and serology in adolescents. A retrospective respiratory questionnaire and anti-pertussis toxin immunoglobulin G measurement was undertaken in a convenience sample of adolescents and was repeated one year later. The US Centers for Disease Control clinical case definition of pertussis was used. At least a third of coughing illnesses met the CDC clinical case definition. Symptoms correlated with serology. Pertussis was endemic with a high annual incidence of new infections.