Objective - A study of subjects with known atrial fibrillation (AF) in a Swedish community. Design - A survey of subjects with present, or previous, AF (at 30 September 1998) identified through medical records. Setting - A community in the Stockholm Metropolitan area. Results - Altogether 230 subjects, mean age 73 years, with a history of AF were identified (140 men and 90 women).One-hundred-and-fortynine patients were identified as having chronic, irreversible AF (65%). Of those with chronic AF, heart failure was noted in 53%, a valvular disease in 8%, hypertension in 32%, coronary heart disease in 36%, diabetes in 17% and an earlier ischaemic cerebrovascular episode in 30%. Hypertension was found as a significant factor for earlier ischaemic cerebrovascular episodes (OR 2.45, 95% CI 1.20?5.19). Anticoagulant treatment was prescribed in 32% out of those with chronic AF. The estimated overall occurrence of subjects with present, or a history of, AF was 0.7% in the community and 1.4% when standardising by age and sex to the whole Swedish population. Conclusion ? AF is a common arrhythmia in Sweden, with an estimated occurrence of 1?1.5%, but despite a high rate of ischaemic cerebrovascular events in chronic AF (30%) a low prescription of anticoagulants.