Objective: To measure the prevalence of chronic obstructive pulmonary disease (COPD) among people aged 40 years or older in Australia. Design, setting and participants: A cross-sectional study of people in the community aged Ã¢Â‰Â¥40 years, selected at random using electoral rolls, in six sites chosen to reflect the sociodemographic and geographic diversity of Australia, conducted between 2006 and 2010. Standardised questionnaires were administered by interview. Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and the FEV1/FVC ratio were measured by spirometry, before and after bronchodilator administration. Main outcome measure: Prevalence of COPD, classified according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2006 criteria. Results: Complete data were available for 1620 men (participation rate, 26%) and 1737 women (participation rate, 28%). The prevalence of GOLD Stage II or higher COPD (defined as post-bronchodilator FEV1/FVC ratio < 0.70 and FEV1 <80% predicted) was 7.5% (95% CI, 5.7%-9.4%) among people aged Ã¢Â‰Â¥40 years, and 29.2% (95% CI, 18.1%-40.2%) among those aged Ã¢Â‰Â¥75 years. Among people aged Ã¢Â‰Â¥40 years, the prevalence of wheeze in the past 12 months was 30.0% (95% CI, 27.5%-32.5%), and prevalence of shortness of breath when hurrying on the level or climbing a slight hill was 25.2% (95% CI, 22.7%-27.6%). Conclusions: Symptoms and spirometric evidence of COPD are common among people aged 40 years or older and increase with age. Further research is needed to better understand the diagnosis and management of COPD in Australia, along with continuing efforts to prevent the disease.