Studies of the prevalence of asthma should be supported by objective markers. We aimed to measure the prevalence of childhood asthma in a particular area and age group using a questionnaire, and to compare the results with the rates of asthma diagnosed by objective measures. All students aged 13-14 (n=1511) in Kemalpasa, Izmir, were included in the study. Children whose responses on the ISAAC Phase-I Questionnaire revealed current wheezing were invited to the district health center. The prevalence of clinically proven asthma (current wheezing supported by objective markers) was investigated. The questionnaire was answered by 1373 (90.87%) students. Current wheezing was indicated in 428 children (31.0%), significantly more in girls than in boys (p<0.05). However, the prevalence of clinically proven asthma decreased by 42.5% when using objective markers. This study provided important epidemiologic information about the prevalence of asthma as indicated by questionnaires as opposed to that indicated by objective measures, especially in countries where the language lacks a word for "wheezing."