The aim of this study was to determine the prevalence of asthma, allergic rhinitis and their related symptoms in Istanbul and to investigate the effect of socioeconomic status on the prevalence of asthma and allergic rhinitis and whether there are differences between the prevalence of childhood asthma in the same and different regions as found in previous studies and our own. The study period was the 1996-1997 school year in three primary schools in Istanbul. For proportional representation of high, middle, and low socioeconomic levels, the schools were selected from three different regions of Istanbul. A translated version of the International Study of Asthma and Allergies in Childhood (ISAAC) was used. The questionnaire was distributed to the parents of 2600 students aged 6-15 years. All of the 2276 children whose parents responded were included in the survey. The overall cumulative and current prevalences of wheezing were 13.7 and 7.2% respectively and the overall cumulative prevalence of allergic rhinitis was 17.6%. There was no statistically significant difference between asthmatics and non-asthmatics by sex, socioeconomic status and passive smoking. Family history of atopy was found to be significantly higher in asthmatics. Although there are differences in the results of studies concerning the prevalence of asthma and allergic rhinitis not only between different countries but also between different regions of the same city, by using a standardized international method, the actual values may be obtained.