Background : Atrial fibrillation (AF) is a common arrhythmia that is a potent independent risk factor for stroke. The incidences of AF increase with age and most affected people have underlying heart disease. In the Framingham Study, the most common cardiac precursors of AF were heart failure, myocardial infarction, and valvular heart disease. In recent studies, TSH, free T4 and metabolic syndrome were well correlated with increased risk of AF. This study was aimed to find predicting risk factors for newly-developed AF in persons received screening test for general health. Subjects & Methods : We retrospectively analyzed 16629 adults (male 10740/female 5889) who repeatedly received screening test for general health at Samsung Medical Center between March, 2001 and June, 2006 ( mean follow up duration : 44 months ). Initial baseline characteristics included answered questionnaires, blood pressure, electrocardiogram (ECG), and blood chemistry test etc. We compared control persons who had no AF on serial screening and persons who have newly developed AF on serial screening. Data analysis was done by SPSS 11.5 for Windows. Results: The incidence of newly-developed AF was 0.09% in persons younger than 45 yrs old, 0.35% between 45 to 54 yrs old, 0.5% between 55 to 64 yrs old and 1.06% in persons older than 65 yrs old. In univariate analysis, male, old age, history of coronary artery disease, hypertensive drug treated state, LA enlargement on EKG were associated with an increased risk of newly-developed AF. In multivariate analysis, risk factors of AF were male (odds ratio, OR 4.37; 95% confidence interval [CI] : 1.856 to 10.290; p=0.001), age (OR 1.050; 95% CI:1.020 to 1.080; p=0.001), history of coronary artery disease (OR 3.67; 95% CI:1.383 to 9.776; p=0.009) and LA enlargement on EKG(OR 4.539; 95% CI:1.755 to 11.738; p=0.002). Thyroid function test and metabolic syndrome were not associated with risk factors for newly-developed AF. Conclusion: Predicting risk factors for newly-developed AF in persons received screening test for general health were male, age, history of coronary artery disease and LA enlargement on EKG.