Aims To show non-inferiority of the 67- or 87 μm thick, sirolimus-eluting Orsiro drug eluting stent (DES) to the 122 μm thick, biolimus-eluting Nobori DES regarding size of vessel lumen outside the stent at 13-month follow-up. Methods and results This study was a substudy to the SORT-OUT VII trial, a prospective, 1:1-randomized, comparison of the two stents in patients with stable coronary artery disease or acute coronary syndrome. Optical coherence tomography was acquired after percutaneous coronary intervention and at 13-month follow-up. The substudy was powered to access non-inferiority (' " = 0.60 mm 2) of the Orsiro DES to the Nobori DES for the primary endpoint of mean extra stent lumen (ESL) i.e. vessel lumen outside the stent at 13-month follow-up. We randomized 124 patients to Orsiro (n = 60) or Nobori (n = 64). Due to a difference in the one-sided 95%-confidence interval of 0.26 mm 2, but increased to 0.82 mm 2 after appropriate log-transformation, it could not be rejected that Orsiro exceeded the non-inferiority limit. Testing for superiority, Orsiro had a significantly larger mean ESL at follow-up (Orsiro: 0.11 mm 2 [0.02;0.30] mm 2, Nobori: 0.03 mm 2 [0.00;0.17] mm 2, P = 0.04). Stent strut coverage was, Orsiro: 97.6 % [93.8;99.4]%, and Nobori: 96.3 % [90.5;98,6]% (P = 0.13). Conclusion Orsiro DES had a significantly larger mean ESL at follow-up and it could not be excluded that Orsiro exceeded the limit for non-inferiority. Nobori DES had a more heterogeneous distribution of neointima but stent strut coverage did not differ significantly between the two stents.