To identify an early, simple, noninvasive predictor of left main (LM) or 3-vessel disease (3-VD), we retrospectively studied clinical variables on admission in 310 patients with acute coronary syndromes with non-ST-segment elevation. Univariate analysis indicated that many factors were related to LM/3-VD. Multivariate analysis showed that ST-segment elevation in lead aVR of >/=0.5 mm was the strongest predictor of LM/3-VD, followed by positive troponin T (odds ratio 19.7, p <0.001, and odds ratio 3.08, p = 0.048, respectively). ST-segment elevation in lead aVR of >/=0.5 mm and positive troponin T identified LM/3-VD with sensitivities of 78% and 62%, specificities of 86% and 59%, positive predictive values of 57% and 26%, and negative predictive values of 95% and 87%, respectively (p <0.05). Our findings suggest that in patients with non-ST-segment elevation acute coronary syndromes, ST-segment elevation in lead aVR of >/=0.5 mm and positive troponin T on admission (especially the former) are useful predictors of LM/3-VD.