We sought to investigate the utilization of prasugrel and its association with outcomes relative to clopidogrel in three typical subgroups of ACS in a real-world setting. Prasugrel is superior to clopidogrel for reducing risk of ischemic events in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI), but is associated with an increased risk of bleeding complications. PROMETHEUS was a retrospective multicenter observational study of 19,913 ACS patients undergoing PCI from 8 centers in the United States between 2010 and 2013. Major adverse cardiovascular events (MACE) were defined as a composite of all-cause mortality, myocardial infarction, stroke or unplanned revascularization. The study cohort included 3285 (16.5%) patients with ST-segment elevation myocardial infarction (STEMI), 5412 (27.2%) patients with NSTEMI and 11,216 (56.3%) patients with unstable angina (UA). The frequency of prasugrel use at discharge was highest in STEMI and lowest in UA patients, 27.3% versus 22.2% versus 18.9% (p<0.001). Use of prasugrel vs clopidogrel was associated with a lower rate of MACE in STEMI, NSTEMI, or UA at 1year, but the differences were attenuated for all groups except for patients with UA (adjusted HR 0.81, 95% CI 0.69-0.94, p=0.006) after propensity adjusted analysis. After adjustment, there was no difference in bleeding risk between prasugrel and clopidogrel for all groups at 1year. STEMI patients were more likely to receive prasugrel compared to NSTEMI and UA patients. Prasugrel was associated with reduced adverse outcomes compared with clopidogrel in unadjusted analyses, findings that were largely attenuated upon adjustment and suggest preferential use of prasugrel in low vs high risk patients.