BACKGROUND: In low-risk patients, the zotarolimus-eluting stent has been shown to reduce rates of restenosis without increasing the risk of stent thrombosis. We compared the efficacy and safety of the zotarolimus-eluting stent versus the sirolimus-eluting stent in patients with coronary artery disease who were receiving routine clinical care with no direct follow-up. METHODS: We did a single-blind, all-comer superiority trial in adult patients with chronic stable coronary artery disease or acute coronary syndromes, and at least one target lesion. Patients were treated at one of five percutaneous coronary intervention centres between January, 2006, and August, 2007. Computer-generated block randomisation and a telephone allocation service were used to randomly assign patients to receive the zotarolimus-eluting or the sirolimus-eluting stent. Data for follow-up were obtained from national Danish administrative and health-care registries. The primary endpoint was a composite of major adverse cardiac events within 9 months: cardiac death, myocardial infarction, and target vessel revascularisation. Intention-to-treat analyses were done at 9-month and 18-month follow-up. This trial is registered with ClinicalTrials.gov, number NCT00660478. FINDINGS: 1162 patients (1619 lesions) were assigned to receive the zotarolimus-eluting stent, and 1170 patients (1611 lesions) to receive the sirolimus-eluting stent. 67 patients (72 lesions) had stent failure, and six patients were lost to follow-up. All randomly assigned patients were included in analyses at 9-month follow-up; 2200 patients (94%) had completed 18-month follow-up by the time of our assessment. At 9 months, the primary endpoint had occurred in a higher proportion of patients treated with the zotarolimus-eluting stent than in those treated with the sirolimus-eluting stent (72 [6%] vs 34 [3%]; HR 2.15, 95% CI 1.43-3.23; p=0.0002). At 18-month follow-up, this difference was sustained (113 [10%] vs 53 [5%]; 2.19, 1.58-3.04; p<0.0001). For patients receiving the zotarolimus-eluting stent and those receiving the sirolimus-eluting stent, all cause-mortality was similar at 9-month follow-up (25 [2%] vs 18 [2%]; 1.40, 0.76-2.56; p=0.28), but was significantly different at 18-month follow-up (51 [4%] vs 32 [3%]; 1.61, 1.03-2.50; p=0.035). INTERPRETATION: The sirolimus-eluting stent is superior to the zotarolimus-eluting stent for patients receiving routine clinical care. FUNDING: Cordis and Medtronic.