Recent studies have suggested that proton pump inhibitors (PPIs) attenuate the benefits of clopidogrel. The clinical relevance of this interaction in patients who have undergone percutaneous coronary intervention (PCI) is unknown. We hypothesized that post-PCI patients discharged on clopidogrel will have higher cardiovascular events if concomitant PPI therapy is used. To determine whether post-PCI patients discharged on clopidogrel will have higher cardiovascular events if concomitant PPI therapy is used. We reviewed the medical records of all the patients discharged on clopidogrel who underwent PCI from January 2003 to August 2004. The primary outcome studied was a major adverse cardiovascular event (MACE), which was defined as a composite of death, myocardial infarction, and target vessel failure. Of the 315 post-PCI patients who were discharged on clopidogrel, 72 were discharged on PPI. During a mean follow-up period of 50 months, patients discharged on concomitant clopidogrel-PPI therapy had a MACE rate of 56% (vs. 38% in the clopidogrel alone group) (P = 0.025) and had 95% excess risk of MACE. Concomitant use of clopidogrel and PPI in post-PCI patients is associated with a higher risk of MACE. This suggests that PPIs may attenuate clopidogrel’s beneficial antiplatelet effect, which is crucial after PCI. Prospective randomized studies are warranted to provide definitive evidence for this interaction.