We sought to describe the prevalence, incidence, risk factors and treatment (according to stroke risk) of atrial fibrillation (AF) in the national, population-based Australian Diabetes, Obesity and Lifestyle (AusDiab) study cohort.ECG data were available from 8273/11,247 participants of AusDiab study in 1999/2000 and from 5422 participants in 2004/2005. Minnesota coding was used to identify prevalent and incident cases of AF.90 prevalent cases of AF (14.1 per 1000) comprising 56 men (mean age 70.5 ± 1.9 years) and 34 women (aged 78.3 ± 1.2 years) were identified in 1999-2000. AF prevalence was associated with sedentary behaviour versus physically active (PR 2.0, 95% CI 1.2-3.6). 53 incident cases of AF (2.0, 95%, CI 1.5-2.6 per 1000 person-year) were subsequently identified in 2004-2005. Increased risk of incident AF was associated with male sex, obesity, history of angina, myocardial infarction and stroke. Both increased weight gain and increased weight loss appeared to be associated with increased risks of developing AF in women, while no obvious association was observed in men. Despite their high risk for stroke, anti-thrombotic therapy was observed in only 39.3% of participants with CHA2DS2-VASC scores ≥ 2.This study contributes to a better understanding of the AF burden. With the ageing population, coordinated efforts will be needed to anticipate the future health care costs related to AF and its impacts on the health care system. This will include appropriate application of anti-thrombotic therapy according to risk of thrombo-embolic events.