Anomalous origin of the left main coronary artery from the right sinus (ALMCA) is a rare entity associated with an increased risk for sudden cardiac death. Although transthoracic echocardiography often is the primary screening tool for the diagnosis, its accuracy remains undefined, resulting in the use of more expensive methods such as cardiac catheterization and magnetic resonance imaging when clinical suspicion exists. This report aims to describe a novel echocardiographic screening method for detecting ALMCA and to apply it retrospectively for patients with confirmed findings intraoperatively and/or on autopsy. All patients with a confirmed diagnosis of ALMCA who presented to our institution from 2004 to 2012 were included in the study. Eight patients had adequate images, including two patients with an initial diagnosis of normal coronary origins. A control group consisted of 35 patients with normal coronaries shown by echocardiogram. Five of these patients had normal coronary artery origins confirmed by magnetic resonance imaging (MRI). Echocardiographic images were reviewed, and the left main coronary was identified in the parasternal long-axis view between the aorta and pulmonary trunk. The angle of the left main coronary course was measured. In patients with ALMCA, the proximal course of the vessel was steeper as it coursed posteriorly. In contrast, the course was almost horizontal in patients with normal coronary origins. Based on these findings, a cutoff angle of 28° is proposed. In the parasternal long-axis view, ALMCA can be identified by its anomalous proximal course. This screening method is reliable and increases the accuracy of transthoracic echocardiograms.