All 98 participating institutions approved the study protocol. Case report forms (CRFs) were collected for each patient who started treatment with prasugrel at least 1 month before the end of the study period, between 27 May 2014 and 26 January 2015. Because all patients were to be followed up until the end of the study period (26 January 2015) regardless of completion or discontinuation of prasugrel treatment, the observation period varied for each patient. Patients with ACS who were to undergo or had recently undergone PCI and had started prasugrel treatment at least 1 month before the end of the study period were included in this study.