Objective: To report the agreement between gray-scale intravascular ultrasound (GS-IVUS) and optical coherence tomography (OCT) in assessing the bioresorbable vascular scaffolds (BVS) structures and their respective reproducibility. Background: BVS are composed of an erodible polymer. Ultrasound and light signals backscattered from polymeric material differs from metallic stents using GS-IVUS and OCT. Methods: Forty-five patients included in the ABSORB trial were treated with a 3.0 × 18 mm BVS and imaged with GS-IVUS 20 MHz and OCT post-implantation. Qualitative (ISA, side-branch struts, protrusion, and dissections) and quantitative (number of struts, lumen, and scaffold area) measurements were assessed by two investigators. The agreement and the inter- and intraobserver reproducibility were investigated using the kappa (κ) and the interclass correlation coefficient (ICC). Results: GS-IVUS and OCT agreement was predominantly poor at a lesion, frame, and strut level analysis (κ and ICC <0.4) for qualitative measurements. GS-IVUS demonstrated a reduced ability to detect cross-sections with ISA (4.5% vs. 20.6%), side-branch (SB) struts (6.3% vs. 7.8%), protrusions (3.2% vs. 9.6%), and dissections (0.2% vs. 9.0%) compared with OCT. GS-IVUS reproducibility was poor–moderate (κ and ICC <0.6) except for ISA and SB-struts (κ and ICC between 0.2 and 0.75). OCT showed an excellent reproducibility (κ and ICC > 0.75) except for the assessment of tissue protrusion (κ and ICC between 0.47 and 0.94). GS-IVUS reproducibility was poor–moderate (ICC ≤ 0.5) in assessing the number of struts but excellent with OCT (ICC > 0.85). The reproducibility to assess lumen and scaffold areas was excellent using both techniques (ICC > 0.85). Conclusions: GS-IVUS has a poor capacity to detect qualitative findings post-BVS implantation and its reproducibility is low compared with OCT. The use of GS-IVUS should be limited when assessing lumen and scaffold areas. © 2011 Wiley Periodicals, Inc.