OBJECTIVE Virtual histology-intravascular ultrasound (VH-IVUS) studies on early-stage fibroatheroma, the probable precursor lesion of progression to thin-cap fibroatheroma (TCFA), have only rarely been done in man. We investigated the progression and observational frequency of fibroatheromas, and compared plaque components between early-stage and advance-staged fibroatheromas in the general population. METHODS We assessed coronary fibroatheromas using VH-IVUS and histopathologic analysis of 109 coronary lesions from 40 autopsied cases that were not due to sudden cardiac death (NSCD cases). Fibroatheromas were grouped into early fibroatheroma, late fibroatheroma, thick-cap fibroatheroma (TkCFA), and thin-cap fibroatheroma. RESULTS Mean patient age was 45+/-11 years old and 71% were males. Of 109 lesions, 27% were early fibroatheromas, 53% late fibroatheromas, 9% TkCFA, and 11% TCFA. VH-IVUS showed that there was relatively less fibrotic and fibrofatty plaque and more dense calcium deposits as fibroatheromas progressed. Furthermore, the relative amounts of fibrotic and fibrofatty plaque decreased (r=0.773, p<0.001 and r=0.538, p<0.001, respectively) as the necrotic core increased, while the relative area of dense calcium increased (r=0.665, p<0.001) as the size of the necrotic core increased. CONCLUSIONS Of NSCD cases in Korea, 27% were early fibroatheromas, 53% were late fibroatheromas, 9% were TkCFA, and 11% were TCFA. Advance-staged fibroatheromas show more necrotic core volume and more dense calcium than small, early-stage fibroatheromas.