Coronary artery calcium indicates atherosclerosis. Ultrafast computed tomography (CT) can noninvasively visualize and quantify coronary calcium, permitting the natural history of calcified plaque to be studied. This pilot study evaluates the ability of ultrafast CT to follow the progression of calcified plaque within the coronary arteries in patients with and without obstructive coronary artery disease (CAD). Twenty-five subjects had serial ultrafast CT scans of the coronary arteries a mean of 406 days apart. Changes in the number of calcific deposits, calcified plaque area and volume, calcium density and total calcium score were measured. In the 20 patients with calcium on the first study, there were statistically significant increases in mean peak CT number, total calcified plaque volume, total calcified plaque area and total calcium score (p less than 0.0001 for all). Subjects with proved obstructive CAD (n = 10) on angiography had a 48% increase in calcified plaque volume compared with 22% in asymptomatic subjects (n = 10). Comparison of serial studies showed that smaller calcific deposits often coalesced into single larger calcific deposits. Ninety-eight percent (235 of 241) of deposits identified on the first study were accounted for on the second study. Patients with obstructive CAD had a higher number of new calcific deposits than did those in the asymptomatic group (55 vs 18, p = 0.058). Serial ultrafast CT accurately tracks the progression of coronary artery calcium. It is a useful technique for assessing changes in calcified plaque formation in both asymptomatic subjects and in patients with obstructive CAD. It may be useful for studying the natural history of CAD and the effects of intervention on the course of CAD.