Increasing asthma prevalence in a rural New Zealand adolescent population: 1975-89. A survey of asthma symptoms and spirometry in 435 adolescent schoolchildren was undertaken in 1989 in a rural, largely Maori population. The survey questionnaires were identical to those used in a 1975 survey at the same school. The prevalence of reported asthma or wheeze significantly increased from 26.2% to 34.0%. This increase occurred in groups reporting asthma, and also those reporting wheeze unassociated with colds, but without a previous diagnosis of asthma. There was a tendency for a rise in reported wheeze in Europeans (24.3% to 27.4%) and a significant rise in Maoris (27.1% to 36.2%). The reclassification of other respiratory problems did not account for the increase. Data from this study provides evidence that there has been a rise in the prevalence of asthma in this New Zealand population over a time period of 14 years. 