Of 634 consecutive patients who had percutaneous coronary intervention (PCI) for acute coronary syndromes, 34 (5%) had major bleeding after PCI, 253 (40%) had minor bleeding after PCI, and 347 (55%) had no bleeding after PCI. Significant independent risk factors for major bleeding after PCI were increased troponin I level (P = 0.004; odds ratio [OR] = 4.7), prior coronary artery disease (P = 0.029; OR = 3.7), platelet glycoprotein IIb/IIIa inhibitors (P = 0.002; OR = 9.8), glomerular filtration rate (GFR) <30 versus >or=60 mL/min/1.73 m(2) (P < 0.0001; OR = 39.7), GFR 30-59 versus >or=60 mL/min/1.73 m(2) (P = 0.0001; OR = 9.4), and clopidogrel loading dose >300 mg (P = 0.0001; OR = 8.9). Significant independent risk factors for minor bleeding after PCI were increased troponin I level (P = 0.0004; OR = 2.1), platelet glycoprotein IIb/IIIa inhibitors (P = 0.039; OR = 2.4), GFR 30-59 versus >or=60 mL/min/1.73 m(2) (P < 0.0001; OR = 2.5), thrombolytics (P = 0.01; OR = 2.7), clopidogrel loading dose >300 mg (P < 0.0001; OR = 4.2), and systolic blood pressure during PCI (P < 0.0001; OR = 1.03 per mm Hg). In-hospital deaths included 5 of 34 patients (15%) with major bleeding, none of 253 patients (0%) with minor bleeding, and none of 347 patients (0%) with no bleeding (P < 0.0001). Hospital duration was 11.0 days in patients with major bleeding, 3.4 days in patients with minor bleeding, and 1.8 days in patients with no bleeding (P < 0.0001).