BACKGROUND: Despite several randomized controlled trials and meta-analyses, the ideal anticoagulant for patients undergoing primary percutaneous coronary intervention (PCI) remains controversial. We performed an updated meta-analysis including recently reported randomized clinical trials that compare bivalirudin and heparin with or without provisional administration of a glycoprotein IIb/IIIa inhibitor (GPI) for primary PCI. METHODS AND RESULTS: Scientific databases and Web sites were searched for randomized clinical trials. Data from 6 trials involving 14,095 patients were included. The pooled risk ratios (RRs) were calculated using random-effects models. Moderator analyses examined the impact of routine use of GPI, radial access, and P2Y12 inhibitors on safety outcomes. At 30 days, patients receiving bivalirudin had rates of major adverse cardiac events similar to those receiving heparin with or without provisional GPI (RR 1.02, 95% CI 0.87-1.19, P = .800), myocardial infarction (RR 1.41, 95% CI 0.94-2.11, P = .089), target vessel revascularization (RR 1.37, 95% CI 0.91-2.04, P = .122), and net adverse clinical events (RR 0.81, 95% CI 0.64-1.01, P = .069). However, bivalirudin use decreased the risk of all-cause mortality (RR 0.81, 95% CI 0.67-0.99, P = .041) and cardiac mortality (RR 0.68, 95% CI 0.51-0.91, P = .009) at 30 days, There were higher rates of acute stent thrombosis (RR 3.31, 95% CI 1.79-6.10, P < .001) in patients receiving bivalirudin. Bivalirudin use also decreased the risk of major bleeding at 30 days by 37% (RR 0.63, 95% CI 0.44-0.90, P = .012), but bleeding risk varied depending on routine GPI use with heparin (RR 0.44, 95% CI 0.23-0.81, P = .009) vs bailout (RR 0.73, 95% CI 0.42-1.25, P = .252), predominantly radial access (RR 0.54, 95% CI 0.25-1.15, P = .114) vs non-radial access (RR 0.60, 95% CI 0.36-0.99, P = .049), and second-generation P2Y12 inhibitor use with bivalirudin (RR 0.70, 95% CI 0.40-1.24, P = .226) vs clopidogrel use (RR 0.39, 95% CI 0.18-0.85, P = .018). CONCLUSIONS: In primary PCI, relative to heparin, bivalirudin reduces the risk for all-cause mortality, cardiac mortality, and major bleeding but yields similar rates of major adverse cardiac event and net adverse clinical event at 30 days. However, the benefit of a reduction in bleeding with bivalirudin appears to be modulated by the concurrent administration of second-generation P2Y12 inhibitors with bivalirudin, using radial access, and avoiding routine GPI use with heparin.