The aim of the present study is to determine the prevalence of asthma and allergic diseases among schoolchildren aged 6-14 years in the State of Qatar, based on a questionnaire designed by the International Study of Asthma and Allergy in Childhood (ISAAC). Across-sectional study of 3,283 school children living in both urban and rural areas (average age, 9.03 +/- 1.99 years; 52.3% boys and 47.7% girls) was conducted between February 2003-February 2004. The population sample had a high prevalence of diagnosed asthma (19.8%), allergic rhinitis (30.5%), eczema (22.5%), and chest infection (11.9%). The frequency of asthma, allergic rhinitis, and eczema among parents reflected the same pattern as seen in their children. Overall, males had more asthma, allergic rhinitis, and chest infections than females. In general, the prevalence rate of asthma and allergic rhinitis decreased with age. The prevalence rate of asthma was significantly higher in mothers (11.8%) than in fathers (9.0%), but the frequency of allergic rhinitis symptoms was comparable (mothers, 18.5%; fathers, 17.5%). The prevalence rate of asthma (19.8%) in Qatari schoolchildren is very close to that in the neighboring Gulf country, Oman (20.7%), and higher than in some developing countries. Geneticfactors related to the high rates of consanguinity may play an important role in the high prevalence rates noted in the Qatari population, but changes in lifestyle and environmental factors cannot be discounted as possible causes of the high prevalence noted in this study.