BACKGROUND Glistening yellow coronary plaques (GY) seen on angioscopy are considered vulnerable to disruption. Collagen fiber (CF) is the main substance that protects coronary plaques against mechanical stress. Therefore, whether angioscopically defined vulnerable plaques correlate with those defined histologically was investigated. RESULTS One hundred and thirty-two excised human coronary plaques were classified by angioscopy into 19 GY, 49 non-glistening yellow plaques (non-GY) and 64 white plaques, and their relation to CF density was examined. CF-dense (>15/100 µm), CF-loose (>5 and <15/100 µm), and CF-scanty (<5/100 µm) plaques were hypothesized to be stable, relatively stable, and vulnerable, respectively. Histologically the plaques were classified into non-lipid deposition, superficial lipid deposition and diffuse lipid deposition groups; the diffuse lipid deposition group was classified into necrotic core (NC) and non-NC types. Nineteen GY were composed of 4 with superficial lipid deposition, 4 with non-NC type of diffuse lipid deposition, and 11 with NC type. Sixteen (84%) of these were CF scanty. Forty-nine (100%) of non-GY and 57 (89%) of white plaques were CF dense or CF loose The sensitivity, specificity and predictive value of GY in detecting histologically vulnerable plaques were 90%, 97% and 84%, respectively, indicating that GY represented histologically vulnerable plaques. CONCLUSIONS These pathohistological characteristics might indicate that GY, less-protected plaques against mechanical stress, are vulnerable plaques.