Histopathological data correlated the presence of thin-cap fibroatheroma (TCFA) with adverse cardiovascular events. Intravascular optical coherence tomography (iOCT) is currently the only imaging modality with sufficiently high axial resolution (∼15 μm) that allows direct fibrous-cap (FC) assessment in vivo. iOCT quantification of TCFA has been validated, but the assessment of a single cross-sectional image does not depict the complexity of the atherosclerotic plaque. We present two cases that illustrate the importance of three-dimensional volumetric quantification of the FC capitalizing on the properties of frequency-domain iOCT. © 2012 Wiley Periodicals, Inc.