To determine the prevalence of asthma in Victorian adults, we carried out a cross-sectional postal survey utilising a new screening questionnaire which gathered data on self reported respiratory symptoms, whether asthma had been diagnosed and, if so, how it had been treated. Questionnaires were returned by 2198 (72%) of 3095 adults selected randomly from the Victorian electoral roll, an adequate response rate. The reported prevalences of individual asthmatic symptoms in the last 12 months ranged from 8% for nocturnal wheeze to 22% for current wheeze. Thirteen per cent of respondents had ever had asthma, 7% had experienced an attack within the last 12 months and 6% were currently taking medication. The high prevalence of asthma revealed by our study has major implications for the planning of health services.