OBJECTIVE To briefly review the role of calcium in the pathophysiology of atherosclerosis and to comprehensively review and analyze studies of coronary artery calcium detected by electron-beam computed tomography (CT). METHODS The English-language literature located through MEDLINE and Current Contents. METHODS All studies of electron-beam CT in symptomatic and asymptomatic patients with and without known coronary artery disease were selected. METHODS Significant findings on the association of cardiac risk factors and angiographically evident coronary artery disease with coronary artery calcium detected on electron-beam CT were compared. Prospective data on clinical outcomes in patients with coronary artery calcium were assessed. RESULTS Coronary artery calcium is common in patients with known coronary artery disease or risk factors for coronary artery disease, and it becomes more common with increasing age. Coronary artery calcium detected by electron-beam CT is a sensitive but not a specific indicator of angiographically evident atherosclerosis; sensitivity is increased and specificity is decreased for angiographically significant disease. Test characteristics can be adjusted to improve specificity at the cost of sensitivity. Very limited data suggest that patients with coronary artery calcium are more likely to have cardiac events. CONCLUSIONS Electron-beam CT is a promising new tool for the evaluation of coronary artery disease because patients who have coronary artery calcium are likely to have angiographically evident atherosclerosis. However, too few data currently exist to support the broad use of this tool in clinical decision making during the evaluation of patients with known or suspected coronary artery disease.