Background: In patients with non-ST-segment elevation acute coronary syndromes (NSTE-ACS), identification of left main and/or 3-vessel disease (LM/3VD) is crucial for deciding whether to initiate early treatment with clopidogrel, which can increase the risk of surgical bleeding.Methods and Results: On admission, the clinical factors of 150 patients with NSTE-ACS, who underwent coronary angiography, were evaluated. ST-segment shifts and the widest QRS duration were measured on an admission 12-lead electrocardiogram. Sixty-seven patients had LM/3VD. Univariate analysis indicated that many factors were related to LM/3VD. On multivariate analysis, QRS duration (P<0.01) and the degree of ST-segment elevation in lead aVR (P<0.01), were independent predictors of LM/3VD.. A QRS duration of >90 ms and a ST-segment elevation in lead aVR of ≥0.5 mm, identified LM/3VD with sensitivities of 67% and 77%,and specificities of 57% and 65%, respectively.