Coronary artery calcium is a marker of atherosclerosis in asymptomatic subjects. Ultrafast computed tomography (CT) can detect and quantify coronary calcium, simply and noninvasively, with greater sensitivity than can other techniques. The prevalence and extent of coronary calcium in a large population of asymptomatic men and women were measured and compared. Coronary calcium studies were performed in an asymptomatic population of 1,396 male and 502 female subjects (age range 14 to 88 years). The prevalence of calcium, and the distribution of total calcium scores (which reflect the amount of calcium present) were determined and compared for men and women at 5- and 10-year intervals. The prevalence of calcium in women was half that of men, until the age of 60 years when the difference diminished. The mean total calcium score distributions of men between the ages of 40 and 69 years were virtually identical to those of women between the ages of 50 and 79. The quantitative data obtained by Ultrafast CT showed very close agreement with autopsy studies of coronary calcium. Ultrafast CT is a sensitive technique to measure coronary calcium in both men and women. The differences in prevalence and extent of coronary calcium appear to be parallel to those observed in the clinical incidence of coronary artery disease in men and women. Ultrafast CT may have a greater impact on the treatment of women than of men, because it can be used to provide objective evidence of coronary atherosclerosis.