OBJECTIVE To estimate whether the prevalence of asthma in adults increased over a nine year interval. METHODS Serial cross sectional studies of the population with a protocol that included both subjective and objective measurements. METHODS Busselton, Western Australia. METHODS A random sample of 553 subjects aged 18-55 years in 1981, and of 1028 subjects aged 18-55 years in 1990. METHODS Respiratory symptoms measured by self administered questionnaire, bronchial responsiveness measured by bronchial challenge with histamine, and allergy measured by skin prick tests. RESULTS Symptoms with increased prevalence were those with significant association with allergy in this population. Recent wheeze increased from 17.5% to 28.8% (p < 0.001) and diagnosed asthma increased from 9.0% to 16.3% (p < 0.001). The increase was greatest in subjects less than 30 years old. The prevalence of shortness of breath coming on at rest and of hay fever also increased significantly, but the prevalence of shortness of breath on exertion, chronic cough, bronchial hyperresponsiveness, current asthma (defined as recent wheeze plus bronchial hyperresponsiveness), and allergy did not increase. The severity of bronchial responsiveness did not change significantly in any symptom group. CONCLUSIONS Young adults showed a significant increase in reporting of symptoms related to allergy but not in the prevalence of current asthma. The increase in symptoms may be due to increased awareness of asthma in this community, to changed treatment patterns, or to increased exposures to allergens.