Background and Objectives: Severe ST-segment depression during exercise electrocardiography(ECG) test is regarded as a parameter associated with adverse prognosis and multivessel diseases. However, in some patients, it is not associated with coronary stenosis. Therefore, we determined the incidence and predictors of significant stenosis in patients with severe ST-segment depression during exercise ECG test. Subjects and Methods: The consecutive 139 patients who showed severe (��� 2.0 mm) ST-segment depression during exercise ECG test were derived from the 10,694 patients from February 2002 through November 2007. Clinical factors and electrocardiographic parameters were compared between the two groups with or without significant coronary stenosis. Multivariate logistic regression analysis was performed. Results: Significant coronary stenosis was present in 82 patients (59%) out of 139. Logistic regression analysis for its predictors was as follows. Conclusions: The incidence of significant coronary stenosis in patients with severe ST-segment depression during exercise ECG test was 59% in our series of patients. The clinical and test predictors were ST-segment depression during recovery and at stage II, ST-segment depression in V1~3, I, and aVL, hypertension, typical chest pain, and male gender. It is more reasonable to do the second noninvasive stress test than to move quickly into invasive test in patients without above-mentioned predictors who showed severe ST-segment depression during exercise ECG test.