The association between coronary artery calcification (CAC) and coronary artery disease is well established. The objectives of this article are to define the cross-sectional anatomy of the coronary arteries and to demonstrate the prevalence of CAC as seen on routine computed tomography (CT) of the thorax. A CT scan of a cadaver heart was performed in normal anatomic position. Additionally, a retrospective analysis of 103 consecutive thoracic scans was done by three experienced radiologists. The cross-sectional anatomy of the coronary arteries is described based on both these studies, and the prevalence of coronary calcification from the retrospective review was determined. The left anterior descending was the most commonly calcified artery (43% of all patients) followed in order by the left coronary (37%), circumflex (33%), and right coronary (20%). Seventy-nine percent of patients older than age 65 demonstrated coronary calcification on CT. This prevalence approaches that of reported autopsy series. Knowledge and understanding of the cross-sectional anatomy of coronary arteries is essential for detection of coronary artery calcification. We recommend that the presence of CAC should be reported on all thoracic CT scans because coronary calcification may signal unsuspected coronary artery disease.