Background Although overlapping sirolimus-eluting stents are often used in long lesions during percutaneous coronary intervention, it was not clear how intimal hyperplasia at the overlapping segments compares with that of single-layer sirolimus-eluting stents.Methods Optical coherence tomography (OCT) examinations were performed on 22 patients in whom overlapping sirolimus-eluting stents (SESs) were implanted. OCT images were analyzed off-line after the procedure. Still frames were selected and classified, and the length of overlap, lumen loss, and average neointimal thickness on the strut were measured. The stent strut was classified into well-apposed to vessel wall with apparent neointimal coverage (type A), well-apposed to vessel wall without neointimal coverage (type B), malapposed to the vessel wall without neointimal coverage (type C), and strut located at a major side branch (type D).Results There was no statistically significant difference between strut coverage types within overlapping and non-overlapping segments, but a greater percentage of type C struts were observed within the overlapping segments (5.2% vs 1.4%, P >0.05). Neither neointimal thickness ((175.0±59.9) um vs (168.3±90.2) pm, P=0.715) nor lumen loss ((1.61±0.55) mm2 vs (1.48±0.37) mm2, P=0.397) was statistically different between the two segments. One patient was diagnosed with suspected in-stent thrombosis at 6 months. Although no specific characteristics of thrombosis were seen on the OCT images, a greater number of malapposed struts without neointima coverage were observed.Conclusions About 90% struts were completely covered by neointimal proliferation at 12 months follow-up, and the thicknesses of neointima on overlapping and non-overlapping segments were similar. Most of type C struts at the overlapping segments were found on the inside layer stents. Delayed antiplatelet therapy was beneficial for the patients with incompletely covered struts.