Background:Data evaluating the effects of acute coronary syndrome (ACS) relative to stable coronary artery disease (CAD) on bleeding risk after percutaneous coronary intervention (PCI) are scarce.Methods and Results:From the CREDO-Kyoto Registry Cohort-3, 13,258 patients undergoing first PCI (5,521 ACS; 7,737 stable CAD) were identified. Patients were further stratified according to ACS presentation and Academic Research Consortium High Bleeding Risk (HBR): ACS/HBR: n=2,502; ACS/no-HBR: n=3,019; stable CAD/HBR: n=3,905; and stable CAD/no-HBR: n=3,832. The primary bleeding endpoint was Bleeding Academic Research Consortium 3/5 bleeding, whereas the primary ischemic endpoint was myocardial infarction (MI)/ischemic stroke. Compared with stable CAD, ACS was associated with a significantly higher adjusted risk for bleeding (hazard ratio HR 1.85; 95% confidence interval CI 1.68–2.03; P<0.0001), with a markedly higher risk within 30 days (HR 4.24; 95% CI 3.56–5.06; P<0.0001). Compared with the stable CAD/no-HBR group, the ACS/HBR, no-ACS/HBR, and ACS/no-HBR groups were associated with significantly higher adjusted risks for bleeding, with HRs of 3.05 (95% CI 2.64–3.54; P<0.0001), 1.89 (95% CI 1.66–2.15; P<0.0001), and 1.69 (95% CI 1.45–1.98; P<0.0001), respectively. There was no excess adjusted risk of the ACS relative to stable CAD group for MI/ischemic stroke (HR 1.07; 95% CI 0.94–1.22; P=0.33).Conclusions:Bleeding risk after PCI depended on both ACS presentation and HBR, with a significant effect of ACS within 30 days.