This study compares the prevalence of asthma and sensitization in children from two Swedish regions with different climates: Göteborg on the southwest coast and Kiruna in the northern inland, north of the Arctic Circle. The 412 children of a population-based sample, 203 in Göteborg and 209 in Kiruna, were investigated at age 7-8 and 12-13 years. Questionnaire reports and interviews were obtained from all children at 7-8 years of age, and 192 children were skin-prick tested for common aeroallergens in Göteborg and 205 in Kiruna. At the follow-up, 5 years later, almost all the children were re-investigated. The prevalence of asthma, wheeze, and sensitization had increased with increasing age during the follow-up period. The questionnaire reports revealed that the prevalence of asthma was 8.5% at 12-13 years of age. All children who in the questionnaire reported current asthma, were using asthma medication. The interviews indicated that the prevalence of a clinically significant asthma might be even higher, reaching approximately 12%. Asthma and wheeze were as common in Göteborg as in Kiruna despite large differences in prevalence of sensitization. Sensitization, and especially sensitization to animals, was far more common in Kiruna than in Göteborg. This study shows that asthma and wheeze are increasingly prevalent even in school age children and that sensitization does not necessarily reflect the prevalence of asthma in a population.