We report a case of a young patient in whom a sirolimus-eluting stent was implanted on the culprit left anterior descending coronary artery at primary percutaneous coronary intervention (PCI) for acute myocardial infarction. Nine months later she suffered from a reinfarction due to the late stent thrombosis despite a continuous antiplatelet therapy with aspirin and clopidogrel. A cluster of factors that might have contributed to the development of the stent thrombosis were identified: suboptimal PCI technique, complete stent fracture, and clopidogrel resistance. The obstructed stent was successfully reopened by repeat PCI, while the clopidogrel maintenance dosage was doubled to 150 mg daily for the following year. The further long-term clinical course was uneventful.