Background The choice of optimal drug-eluting stent therapy for patients with diabetes mellitus (DM) undergoing percutaneous coronary intervention remains uncertain. We aimed to assess the long-term clinical outcomes after percutaneous coronary intervention with biodegradable polymer sirolimus-eluting stents (BP-SES) versus durable polymer everolimus-eluting stents (DP-EES) in patients with DM. Methods and Results In a prespecified subgroup analysis of the BIOSCIENCE (Ultrathin Strut Biodegradable Polymer Sirolimus-Eluting Stent Versus Durable Polymer Everolimus-Eluting Stent for Percutaneous Coronary Revascularization) trial (NCT01443104), patients randomly assigned to ultrathin-strut BP-SES or thin-strut DP-EES were stratified according to diabetic status. The primary end point was target lesion failure, a composite of cardiac death, target vessel myocardial infarction, and clinically indicated target lesion revascularization, at 5 years. Among 2119 patients, 486 (22.9%) presented with DM. Compared with individuals without DM, patients with DM were older and had a greater baseline cardiac risk profile. In patients with DM, target lesion failure at 5 years occurred in 74 patients (cumulative incidence, 31.0%) treated with BP-SES and 57 patients (25.8%) treated with DP-EES (risk ratio, 1.23; 95% CI, 0.87-1.73 [P=0.24]). In individuals without DM, target lesion failure at 5 years occurred in 124 patients (16.8%) treated with BP-SES and 132 patients (16.8%) treated with DP-EES (risk ratio, 0.98; 95% CI, 0.77-1.26 [P=0.90; P for interaction=0.31]). Cumulative 5-year incidence rates of cardiac death, target vessel myocardial infarction, clinically indicated target lesion revascularization, and definite stent thrombosis were similar among patients with DM treated with BP-SES or DP-EES. There was no interaction between diabetic status and treatment effect of BP-SES versus DP-EES. Conclusions In a prespecified subgroup analysis of the BIOSCIENCE trial, we found no difference in clinical outcomes throughout 5 years between patients with DM treated with ultrathin-strut BP-SES or thin-strut DP-EES. Clinical Trial Registration URL: https://www.clinicaltrials.gov/. Unique identifier: NCT01443104.