The prevalence of asthma and allergy in children is increasing. In order to investigate time trends, follow-up studies conducted several years apart and with identical study designs are essential. We compared two identical, cross-sectional and questionnaire-based studies of asthma and allergy in north-Norwegian schoolchildren (7-13 years of age). The first study was conducted in 1985 (n = 10,093) and the second in 1995 (n = 8,676). The cumulative incidence was as follows: diagnosed asthma, 8.6% in 1995 vs. 5.1% in 1985, relative risk (RR) = 1.71 (95% CI: 1.53-1.90); allergic rhinoconjunctivitis, 22.1% in 1995 vs. 16.4% in 1985, RR = 1.39 (95% CI: 1.31-1.47); and atopic dermatitis, 19.7% in 1995 vs. 13.2% in 1985, RR = 1.48 (95% CI: 1.39-1.58). The cumulative incidence of allergic rhinoconjunctivitis and atopic dermatitis was higher in children of Sami ethnicity than Norse ethnicity in the 1985 study. Furthermore, although not statistically significant, there was a trend towards a greater increase in the cumulative incidence of diagnosed asthma, symptoms of asthma, allergic rhinoconjunctivitis, and atopic dermatitis from 1985 to 1995 in children of Sami ethnicity than Norse ethnicity. We conclude that there has been a marked increase in the cumulative incidence of asthma and allergy prevalence among schoolchildren in northern Norway from 1985 to 1995.