A cross-sectional survey of a cohort study was carried out between June and December 1994 in Valencia, Spain (population in 1994: 764,293 inhabitants). Two hundred sixty public and private schools randomly selected from the total of schools in Valencia were invited to participate; 3948 children aged 6-7 years cooperated in our study after informed consent was obtained from parents and school director. The survey in Valencia is part of the International Study of Asthma and Allergy in Childhood (ISAAC). Prevalences for asthma, rhinitis and atopic dermatitis were determined and contrasted with socioeconomic status (SES) among children. No statistically significant associations were established between the prevalences of asthma, rhinitis and atopic dermatitis, and SES. However, atopic dermatitis was found to be common among upper class children (21.5 per 100 children). Likewise, significant associations were observed between the severity of atopy (2 or 3 atopic manifestations) and SES (p = 0.000), being greater for lower strata (4.5 per 100 children); for the three SES level significant differences were established (p = 0.008) regarding passive exposure to tobacco smoke in the home.