We describe a direct and accurate method for defining chest radiographic anatomy and use this method to delineate the anatomic composition of the right mediastinal border in an adult population. Intravenous contrast-enhanced computed tomographic scans of the chest and accompanying scout tomograms from 99 adults without previously known or detected cardiopulmonary disease that could potentially distort mediastinal, cardiac, or pulmonary anatomy were retrospectively evaluated. Transverse CT images through the mediastinum were directly referenced to the respective acquisition location on the scout tomogram via the acquisition reference line. The anatomic composition of the right mediastinal border on the scout tomogram was determined by drawing a vertical line tangential to the most lateral right mediastinal structure in each transverse CT image. The lengths and relationships of these structures were tabulated. These results will help to create a consensus among radiologists and other clinicians regarding radiographic anatomy, allowing improved localization of mediastinal pathology and enabling more optimal positioning of vascular and cardiac support devices.