Stent thrombosis (ST) after percutaneous coronary intervention has been the focus of intense interest because of its attendant morbidity and mortality. There is controversy about several facets of the problem. These include the frequency of ST with drug-eluting stents (DES) versus bare-metal stents (BMS), the timing of the event, clinical consequences, risk factors, adjunctive therapy, and new preventive approaches. Information has accrued rapidly from several sources, including randomized controlled clinical trials of DES versus BMS in carefully selected subsets of patients and registry experiences in larger patient groups, which provide a more universal real-world picture. The results from these different data sets are not completely concordant. However, several general conclusions can be made: 1) ST is an infrequent but very severe complication of both BMS and DES; 2) at the present time, during 4 years of follow-up from randomized controlled trials that compared DES and BMS, there is no apparent difference in overall ST frequency, although the time course for occurrence appears to differ, with a relative numeric excess of ST late after DES implant; 3) despite this relative imbalance, no differences in the end points of death or death and infarction between DES and BMS are observed; 4) longer-term follow-up of these patients as well as larger angiographic and clinical subsets of patients who receive this technology outside of randomized trials are required to fully study this issue; and 5) advances in stent platforms for drug elution as well as adjunctive pharmacologic therapy are being evaluated to enhance long-term safety.