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 at cardiology department. Methods: We enrolled consecutively 1883 patients with coronary artery disease from may 2006 to may 2008. 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, C-reactive protein (CRP), pro-brain natriuretic peptides (pro-BNP) and echocardiographic parameters like left ventricular ejection fraction (LVEF), dimension of left atrium and LV, LV mass index and mitral inflow (E) and annulus velocity (E���). Results: Among 1883 patients, 354 patients (18.8 %, mean age 63.2짹12.2 yrs, M/F 200/154) had thyroid dysfunction; subclinical hypothyroidism 4.8% (90/1883), hypothyroidism 0.4%(8/1883), subclinical hyperthyroidism 11.0% (207/1883), and hyperthyroidism 2.6%(49/1883). The patients with thyroid dysfunction had higher incidence of smoker and female compared to those with normal thyroid function. Also, patients with thyroid dysfunction had more increased level of pro-BNP, CRP, LVEF 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 LV systolic and diastolic dysfunction. However, follow up study might be needed.