Coronary artery calcium scanning is a routine test for assessing the severity of atherosclerosis in asymptomatic individuals. This inexpensive, noninvasive test quantifies the calcium deposition in the 4 principal coronary arteries. Correct interpretation is important to the physician (for recommending therapy) and to the patient (for determining his or her lifetime risk of a cardiovascular event). A score of 0 indicates that a cardiovascular event is extremely unlikely in the next 5 years. In contrast, a score greater than 0 portends a coronary event. The higher the score, the greater the risk. Both the arterial location of the calcium and the number of coronary arteries involved alter the interpretation of the calcium score. At any given age, females have significantly lower scores than males. One-third of individuals with scores greater than 1000 will have a cardiovascular event within 3 years. For all elevated calcium scores, aggressive treatment is warranted, including significant lifestyle changes and medications to reduce low-density lipoprotein cholesterol. Understanding the importance of the coronary artery calcium score will result in improved therapy and patient compliance.