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Background: In October 2003, six months after approval of the first drug-eluting coronary stent (CYPHER™ stent), the FDA reported 50 stent-associated hypersensitivity reactions. In November 2003, FDA officials reported that these reactions were probably due to concomitantly prescribed medications. Methods: All adverse device event reports for CYPHER stent associated hypersensitivity- reactions in the FDA’s adverse event reporting system, the published literature, or from RADAR, between April 2003 and June 2004 were reviewed. Causality was evaluated using World Health Organization criteria. Results: Review of FDA reports (n=2,607) identified 161 persons with hypersensitivity symptoms. Fewer than 20 hypersensitivity cases were reported monthly, except for 43 and 42 reports in October and November 2003. Symptoms began within 2 days of stent implantation (21%), between 2 and 7 days (43%) and between 7 and 14 days (19%) following stent implantation and persisted for less than 8 days for 17%, 8–30 days for 29% and > 30 days for 55%. Findings included rash (80%), itching (28%), hives (19%), dyspnea (12%), fever (12%), chest pain (8%), anaphylaxis (7%), joint pain or swelling (7%) and high or low blood pressure (5%). Among persons with rashes, 25% covered the entire body, 21% developed hives, 7% had localized maculopapular eruptions and 4% developed blisters or desquamation. Treatment included emergency interventions (26%) or hospitalization (19%). Outcomes included permanent disability (5%) or death (2%). Aspirin or clopidogrel was discontinued at the time of hypersensitivity onset for 42. Using WHO criteria, clopidogrel, aspirin, ticlopidine and/or the stent itself were classified as possible causes for > 85% of cases. Of 150 events possibly caused by the CYPHER stent, 35 persisted for > 30 days. For 7 probable CYPHER-stent induced hypersensitivity cases identified by RADAR (n=4), the FDA (n=2) or the literature (n=1), symptom onset was < 5 days (n=3) and at 3 weeks, 1 month, 4 months, and 7 months after stent implantation. Findings included rash (n=4), hives (n=1), blisters on both hands (n=1), dyspnea (n=2), eosinophilia (n=1), elevated IgE levels (n=2) and Gallium-67 scan findings at the stent (n=1). Findings did not abate with thienopyridine discontinuation (n=5). Outcomes included resolution of symptoms with hospitalization (n=1) or corticosteroids (n=2), persistent angina (n=1) and subsequent occurrence of fatal cardiac events, with autopsy identification of eosinophilic infiltrates at the stent site (n= 2 patients). Conclusion: Rash, hives, dyspnea and catastrophic cardiac events may represent local and systemic hypersensitivity reactions from the CYPHER-stent. Reporting of these events decreased by > 90% following a FDA advisory that suggested that skin reactions were unrelated to the stent. However, our findings highlight the importance of continued vigilance for hypersensitivity reactions that may represent an early manifestation of a catastrophic hypersensitivity event.