Objective. The measurement of asthma, rhinitis and eczema have been subject of controversy due to lack of a standardized methodology. To test the applicability of a standardized methodology for comparisons of time and space we determined the prevalence of asthma and other allergic diseases in a random sample of schoolchildren (n= 6 238) from 6 to 8 and 11 to 14 years of age living in Cuernavaca, Morelos, Mexico. Material and methods. The methodology proposed by the International Study of Asthma and Allergies in Childhood (ISAAC) to determine prevalence and severity of asthma, rhinitis and eczema was applied. Current and accumulated information on prevalence was obtained by means of a standardized questionnaire answered by the children's parents. Results. The accumulated prevalence of asthma by medical diagnosis and wheezing was 5.8% (5.2-6.4) and 21.8% (20.7-22.9) respectively; prevalence of wheezing in the last 12 months was 8.9% in the group of 6 to 8 years against 6.6% in the 11 to 14 year old group p<0.001. Prevalence of the medical diagnosis of rhinitis was 4.9% (4.3-5.5). Regarding the typical symptoms of rhinitis, in the last 12 months prevalence was 9.6% (6-8 years) and 10.1% (11-14 years). Prevalence of eczema by medical diagnosis was 4.1% (3.6-4.6). Prevalence of eczema symptoms in the last 12 months was 10.1% (6-8 years) and 10.6% (11-14 years). Prevalence of severe asthma symp-