During the school year 1980–81 a survey questionnaire was carried out among schoolchildren aged 7 to 15 years in Oslo. The survey population comprised 39,162 children attending compulsory primary school. The questionnaire was distributed to a random sample of 1772 children in 81 classes, forms 1 to 9, and the response rate was 95%. The prevalence of physician-diagnosis of current and cumulative asthma was 1.6% and 3.1%, respectively. Of those with current asthma 68% used asthma drugs regularly. Occasional wheezing and attacks of breathlessness were reported by 9% and 4%, respectively. Wheezing and breathlessness on exposure to pollen (4.5%), animals (3.1%) and exercise (5.5%) was reported more frequently than physician-diagnosis of asthma. The cumulative prevalence of either hay fever, eczema, urticaria or asthma was 17%. More boys than girls under the age of 12 had a physician-diagnosis of asthma.