Purpose: Thyroid dysfunction has been known as risk factor of cardiovascular disease. Particularly, subclinical hypothyroidism has a greater adverse affect on cardiovascular system. The aim of this study was to evaluate incidence and clinical feature of thyroid dysfunction in patients admitting due to coronary artery disease. Methods: We enrolled consecutively 991 patients with coronary artery disease from may 2006 to may 2007. We excluded patients with prior thyroid dysfunction. We evaluated the laboratory parameters including cell blood count, thyroid stimulating hormone (TSH), free thyroid hormone (FT4), lipid profile, pro-brain natriuretic peptides (pro-BNP) and echocardiographic parameters like left ventricular ejection fraction, LV mass index and mitral inflow (E) and annulus velocity (E���). Results: Among 991 patients, 177 patients (17.9 %, mean age 61.5짹13.6 yrs, M/F 86/91) had thyroid dysfunction; subclinical hypothyroidism 5.1% (51/991), hypothyroidism 0.9%(9/991), subclinical hyperthyroidism 9.5%(94/991), and hyperthyroidism 2.3%(23/991). The patients with thyroid dysfunction had higher incidence of hypertension and acute coronary syndrome compared to those with normal thyroid function. Also, patients with thyroid dysfunction had more increased level of pro-BNP and E/E��� compared to those normal thyroid function. Conclusions: The incidence of thyroid dysfunction might be higher as expected. Thyroid dysfunction seems to be associated with diastolic dysfunction. However, follow up study might be needed.