Coronary artery dilation has been described as an early effect of atherosclerosis. No noninvasive technique has been available to measure coronary size. In this study coronary diameters were measured in 100 asymptomatic subjects (89 men and 11 women, mean age 40 +/- 6 years) by means of ultrafast computed tomography (UFCT), with 3 mm thick ECG gated scans. Subjects without evidence of coronary calcium were studied. The diameter of the left main (LD) and right (RD) coronary arteries were measured. Total coronary diameter, TD = LD + RD, was determined, and univariate analysis was performed with respect to total, high-density lipoprotein and low-density lipoprotein cholesterol, mean blood pressure, age, body surface area, and triglycerides. Mean LD was 4.23 +/- 0.85 mm, and mean RD was 3.06 +/- 1.08 mm. TD increased with body surface area (p < 0.001). No other variable showed any significant effect on TD in this group without evidence of atherosclerosis. UFCT can be used to noninvasively measure coronary artery diameters and may be a useful technique to detect early changes of atherosclerosis in individual patients and in population studies.