Data on the prevalence of hyperventilation syndrome (HVS) in adolescents are scanty. Objectives: To determine the prevalence of HVS in a population of adolescents with and without asthma, and to verify whether HVS was related to asthma activity. Methods: A population of adolescents was asked to self-complete a questionnaire, including the Nijmegen questionnaire to assess HVS, and a standardized asthma questionnaire. Results: Seven hundred and sixty questionnaires were suitable for analysis. One hundred and twenty subjects (15.8%) were classified as asthmatic. Forty-seven subjects (6.2%) had a Nijmegen score ≥23, which was suggestive of HVS. Symptoms indicative of HVS were ten times more common in subjects with asthma (25%) than in those without asthma (2.5%). Nijmegen score was significantly higher in subjects with lifetime asthma (P < 0.001), current episodic asthma (P < 0.05) and current active asthma (P < 0.001) than in those with no asthma. In the whole population, girls presented HVS more frequently than boys (P < 0.001). There was a significant effect of gender (females, OR 3.2) and status of asthma (lifetime asthma, OR 11.2; current episodic asthma, OR 8.9; current active asthma, OR 41.5) on the probability of suffering from HVS. Conclusions: The prevalence of symptoms indicative of HVS in an unselected population of adolescents was relatively high. Symptoms were more common in girls and in subjects with asthma, and there was a significant effect of asthma activity on the probability of suffering from HVS. Further studies need to be performed in order to validate a screening tool for HVS in both adolescents and asthmatic subjects.