Stent thrombosis (ST) is an infrequent (0.5% to 1.5%) complication of intracoronary stenting, with severe clinical consequences. This multicenter, randomized study evaluated the clinical outcome in 479 patients (598 lesions treated) who underwent elective coronary stenting with a Carbofilm-coated stent (CarboStent) who met prespecified eligibility criteria and were randomly assigned to receive aspirin alone (n = 235) or aspirin plus a thienopyridine antiplatelet regimen (n = 244). Clinical, angiographic, and procedural characteristics were similar between groups. The primary end point was the incidence of 30-day ST; secondary end points included major vascular or bleeding complications within 30 days and death, acute myocardial infarction, and target vessel revascularization at 6 months. ST occurred in 4 patients (1.4%) in the aspirin-only group and in 1 patient (0.3%) in the aspirin-plus-thienopyridine group (relative risk 0.23, 95% confidence interval 0.03 to 2.08, p = NS). After careful review of cases, 89 patients (19%) with protocol deviations were identified. When they were excluded from the analysis, no ST was observed in either group. Secondary end points were reached by 4% of the aspirin-alone group and 8% of the aspirin-plus-thienopyridine group (relative risk 2.35, 95% confidence interval 0.94 to 5.85, p = NS). In conclusion, after optimal intracoronary implantation of the CarboStent, antiplatelet therapy with aspirin alone was safe and provided efficacy comparable to aspirin plus a thienopyridine in the prevention of ST.