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Background: After an initial episode of atrial fibrillation (AF), AF may recur and become permanent. AF progression is associated with higher morbidity and mortality. Understanding the risk factors for permanent AF could help identify people who would benefit most from interventions., Objective: To determine whether body mass index (BMI), diabetes, hypertension, and blood pressure levels are associated with permanent AF among people whose initial AF episode terminated., Design: Population-based inception cohort study., Participants: Enrollees in Group Health, an integrated health care system, aged 30-84 with newly diagnosed AF in 2001-2004, whose initial AF terminated within 6 months and who had at least 6 months of subsequent follow-up (N = 1,385)., Main Measures: Clinical characteristics were determined from medical records. Permanent AF was determined from medical records and ECG and administrative databases. Permanent AF was defined as AF present on two separate occasions 6-36 months apart, without any documented sinus rhythm between the two occasions. Cox proportional hazards models were used to estimate adjusted hazard ratios (HRs)., Key Results: Five-year cumulative incidence of permanent AF was 24 %. Compared with normal BMI (18.5-24.9 kg/m(2)), BMI levels of 25.0-29.9 (overweight), 30.0-34.9 (obese 1), 35.0-39.9 (obese 2), and ≥ 40.0 kg/m(2) (obese 3) were associated with HRs of permanent AF of 1.26 (95 % CI: 0.92, 1.72); 1.35 (0.96, 1.91); 1.50 (0.97, 2.33); and 1.79 (1.13, 2.84), adjusted for age, sex, diabetes, hypertension, blood pressure, coronary heart disease, valvular heart disease, heart failure, and prior stroke. Diabetes, hypertension, and blood pressure were not associated with permanent AF., Conclusions: For people whose initial AF episode terminates, benefits of having lower BMI may include a lower risk of permanent AF. Risk of permanent AF was similar for people with and without diabetes or hypertension and across blood pressure levels.