The general objective of ISAAC (Inter-national Study of Asthma and Allergies in Childhood) is to better know the distribution and risk factors of allergic diseases. The objective of phase I survey, which will be dealt with in this special issue, is to get prevalence figures about asthma, rhinitis and eczema worldwide using a simple and validated questionnaire, In France, 18000 teenagers from the area of Bordeaux Fos l'Etang de Berre, Languedoc-Roussillon, West-Marne and Strasbourg and 8700 children fi om Bordeaux and Strasbourg participated to the survey in 1994 and 1995. In Fos l'Etang de Berre and Strasbourg areas, teenagers answered to a video-questionnaire about asthmatic symptoms following the paper questionnaire. The paper questionnaire was translated from English and back-translated. Reproducibility of the paper questionnaire and comparison of answers provided by teenagers and their parents was studied in a small additionnal survey completed in a sample of 300 adolescents. Data analysis include first a descriptive analysis within each center, then comparison of prevalence figures between centers.