Asthma is more prevalent in Australia than in Europe or North America. As part of the European Community Respiratory Health Survey (ECRHS), we investigated exposure to risk factors for asthma among young adults in Melbourne. During this study, 553 randomly selected and 204 symptomatic participants aged between 20 and 44 years completed a detailed respiratory questionnaire, of whom 675 underwent measurement of bronchial hyperreactivity (BHR) by methacholine challenge and 745 had skin prick tests for atopy. Current asthma, defined as BHR and wheeze in the preceding 12 months, was present in 25.5% of those tested. A family history of asthma was a risk factor for current asthma (maternal asthma odds ratio [OR] 2.4, paternal asthma OR 2.1). Current smokers were 1.7 times more likely to have current asthma. A serious respiratory infection before 5 years of age increased the risk of current asthma 2.3-fold. Atopy on skin testing was also strongly associated with current asthma (OR 5.9). The greatest risks were associated with positive skin tests to Cladosporium, house dust mite, cat and rye grass pollen. We conclude that female gender, maternal asthma, smoking, hayfever, early respiratory infection, occupational exposure and atopy are important risk factors for asthma in young adults.