Introduction: Old age, hypertension, rheumatic valve disease, stroke history, diabetes, and congestive heart failure are known as risk factors of stroke in AF. However, some patients have TE event without risk factors. Hypothesis: We assessed the hypothesis that there would be characteristics in those patients. Methods: 2948 patients, among 16403 AF patients who were registered in KORAF from Nov 2005 to Oct 2007, did not have even one usual risk factor of TE. For 524 patients(53.0짹9.85 year, 383 males) who have analyzable data, patient���s characteristics were analyzed according to development of TE event. Results: Study population consisted of 128(24.4%) first-detected AF, 195(37.2%) paroxysmal AF, 72(13.7%) persistent AF, 53(10.1%) permanent AF, and 32(6.1%) undefined AF. TE event developed in 44(8.4%) patients. Between TE event developers and non-developers, Age, sex, and smoking incidence were not different. Left atrium diameter was not different. Left ventricle ejection fraction was lower(51.4짹15.38 % vs. 57.8%짹12.75 %, p=0.009) and left ventricle end diastolic diameter was larger(53.4짹9.02 mm vs. 46.6짹16.24 mm, p=0.034) in TE event developers. Rate-control was a general treatment strategy(75% in TE developer, 71.8% in TE non-developer, p=0.846). Aspirin was put in 197(37.5 %) patients and warfarin was put in 121(23.0 %) patients. Achievement-percentage of target INR and average INR were not different(37.7 % vs. 27.2%, p=0.302, 2.04 vs. 1.93, p=0.445). Interestingly, TE event incidence in permanent AF was higher than non-permanent AF( 13(16%) vs. 27(7%), p=0.029). Conclusion: It was hard to clarify TE risk factors of Korean AF patients without risk factors. In these riskless patients, anticoagulation strategy was less important, left ventricular function was more important. Further analysis like multivariate regression analysis and follow-up data are needed.