Objectives We performed this study to investigate with optical coherence tomography (OCT) the vascular response after sirolimus-eluting stent (SES) implantation between patients with and those without diabetes mellitus (DM). Background The difference in vascular response after SES implantation between patients with and those without DM has not been fully evaluated with OCT. Methods Optical coherence tomography was performed to examine 74 nonrestenotic SES implanted in 63 patients (32 with DM and 31 without DM) at 9 months after SES implantation. For struts showing neointimal coverage, the neointimal thickness on the luminal side of each strut section was measured, and neointimal characteristics were classified into high, low, and layered signal pattern. Results Baseline patient characteristics and lesion and procedural characteristics data were similar between the 2 groups. In total, 11,422 struts were analyzed. High signal neointima was observed in 90.2 +/- 13.9%, low signal neointima in 7.3 +/- 10.0%, and layered neointima in 2.7 +/- 5.8%/stents. There was higher incidence of low signal neointima (10.5 +/- 10.3% vs. 4.5 +/- 5.6%, p = 0.003), neointimal thickness was larger (median: 106.8 mu m, interquartile range: 79.3 to 130.4 mu m vs. median: 83.5 mu m, interquartile range: 62.3 to 89.3 mu m; p < 0.0001), and neointimal coverage of stent struts was higher (92.1 +/- 6.2% vs. 87.2 +/- 11.9%; p = 0.03) in DM patients. Conclusions High signal neointimal pattern was predominantly observed, and low or layered signal pattern was observed in some cases. In DM patients, low signal neointima was observed with high frequency. Neointimal coverage and neointimal thickness was also higher in DM patients as compared with non-DM patients. (J Am Coll Cardiol Intv 2010;3:1074-9) (C) 2010 by the American College of Cardiology Foundation