Aims To compare the tissue coverage of a hydrophilic polymer-coated zotarolimus-eluting stent (ZES) vs. a fluoropolymercoated everolimus-eluting stent (EES) at 13 months, using optical coherence tomography (OCT) in an 'all-comers' population of patients, in order to clarify the mechanism of eventual differences in the biocompatibility and throm-bogenicity of the devices. Methods and results Patients randomized to angiographic follow-up in the RESOLUTE All Comers trial (NCT00617084) at pre-specified OCT sites underwent OCT follow-up at 13 months. Tissue coverage and apposition were assessed strut by strut, and the results in both treatment groups were compared using multilevel logistic or linear regression, as appropriate, with clustering at three different levels: patient, lesion, and stent. Fifty-eight patients (30 ZES and 28 EES), 72 lesions, 107 stents, and 23 197 struts were analysed. Eight hundred and eighty-seven and 654 uncovered struts (7.4 and 5.8%, P = 0.378), and 216 and 161 malapposed struts (1.8 and 1.4%, P = 0.569) were found in the ZES and EES groups, respectively. The mean thickness of coverage was 116 +/- 99 mu m in ZES and 142 +/- 113 mu m in EES (P = 0.466). No differences in per cent neointimal volume obstruction (12.5 +/- 7.9 vs. 15.0 +/- 10.7%) or other areas-volumetric parameters were found between ZES and EES, respectively. Conclusion No significant differences in tissue coverage, malapposition, or lumen/stent areas and volumes were detected by OCT between the hydrophilic polymer-coated ZES and the fluoropolymer-coated EES at 13-month follow-up.