IMPORTANCE: Bleeding is the most common complication after percutaneous coronary intervention (PCI) and is associated with increased morbidity and health care costs. The incidence of bleeding-related mortality after PCI has not been described in a nationally representative population. Furthermore, the relationships among bleeding risk, bleeding site, and mortality are unclear. OBJECTIVES: To describe the association between bleeding events and in-hospital mortality after PCI and to estimate the adjusted population attributable risk (estimated as the proportion of mortality risk associated with bleeding events), risk difference, and number needed to harm (NNH) for bleeding-related in-hospital mortality after PCI. DESIGN, SETTING, AND PATIENTS: Data from 3,386,688 procedures in the CathPCI Registry performed in the United States between 2004 and 2011 were analyzed. The population attributable risk was calculated after adjustment for baseline demographic, clinical, and procedural variables. To calculate the NNH for bleeding-related mortality, a propensity-matched analysis was performed. MAIN OUTCOME MEASURES: In-hospital mortality. RESULTS: There were 57,246 bleeding events (1.7%) and 22,165 in-hospital deaths (0.65%) in 3,386,688 PCI procedures. The adjusted population attributable risk for mortality related to major bleeding was 12.1% (95% CI, 11.4%-12.7%) in the entire CathPCI cohort. The propensity-matched population consisted of 56,078 procedures with a major bleeding event and 224 312 controls. In this matched cohort, major bleeding was associated with increased in-hospital mortality (5.26% vs 1.87%; risk difference, 3.39% [95% CI, 3.20%-3.59%]; NNH = 29 [95% CI, 28-31]; P < .001). The association between major bleeding and in-hospital mortality was observed in all strata of preprocedural bleeding risk (low: 1.62% vs 0.17%; risk difference, 1.45% [95% CI, 1.13%-1.77%], NNH = 69 [95% CI, 57-88], P < .001; intermediate: 3.27% vs 0.71%; risk difference, 2.56% [95% CI, 2.33%-2.79%], NNH = 39 [95% CI, 36-43], P < .001; and high: 8.16% vs 3.45%; risk difference, 4.71% [95% CI, 4.35%-5.07%], NNH = 21 [95% CI, 20-23], P < .001). Although both access-site and non-access-site bleeding were associated with increased in-hospital mortality (2.73% vs 1.87%; risk difference, 0.86% [95% CI, 0.66%-1.05%], NNH = 117 [95% CI, 95-151], P < .001; and 8.25% vs 1.87%; risk difference, 6.39% [95% CI, 6.04%-6.73%], NNH = 16 [95% CI, 15-17], P < .001, respectively), the NNH was lower for nonaccess bleeding. CONCLUSIONS AND RELEVANCE: In a large registry of patients undergoing PCI, postprocedural bleeding events were associated with increased risk of in-hospital mortality, with an estimated 12.1% of deaths related to bleeding complications.