The prevalence of atopy and asthma, and their association with familial and environmental factors were investigated among 13- to 14-yr-old children living in Brescia, an industrialized town in North Italy. All the 1450 children attending primary school in the town were invited to participate, and 967 of them (66.7%, 493 males) provided a valid questionnaire filled in by their parents at home. We used a modified version of the questionnaire adopted in the Italian Study of Respiratory Disorders in Childhood and Environment, which is an extended version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. Six hundred and twenty-eight subjects underwent skin prick test (SPT), and 308 of them (49%) were positive for at least one of the 12 allergen extracts commonly employed. Ninety-nine children (10.2%) had a physician's diagnosis of asthma - 12.4% of the males and 8.0% of the females (p = 0.03). The prevalence of wheezing in the past 12 months was 6.2%. Atopy was found in 76.8% of the subjects with, and in 45.6% of those without physician's diagnosis of asthma (p < 0.001). Analysis by multiple logistic regression showed an inverse association between physician-diagnosed asthma and female sex (odds ratio, OR = 0.5); presence of relatives in the bedroom in initial years of life (OR = 0.6); attending day care (OR = 0.4) and infant school (OR = 0.4); a positive association with parental history of wheezing (OR = 2.5) and asthma (OR = 3.8); and the child's history of asthmatic bronchitis (OR = 31.9) and atopic eczema (OR = 3.8) in the first 2 yr of life. The strength of the associations did not change when restricting the analysis to atopic asthma. In conclusion, atopy and clinical asthma among 13- to 14-yr-old adolescents are significantly associated with some familial and environmental factors, providing further support for the hygiene hypothesis. Prevalence of atopy, but not of asthma, is high in this industrialized area. The strong association found between atopy and clinical asthma suggests that atopy may play a role in causing asthma in genetically predisposed children only.