The relation between body mass index (BMI) and bleeding after percutaneous coronary intervention (PCI) remains incompletely understood. This study aimed to assess the association between BMI and bleeding and mortality after PCI. The study included 14,178 patients with coronary artery disease treated by PCI. Bleeding within 30 days of PCI was defined using the Bleeding Academic Research Consortium criteria. The primary outcome was 1-year all-cause mortality. BMI quartiles were 14.1 to 24.8 kg/m² (first quartile [Q1]), >24.8 to 27.1 kg/m² (second quartile [Q2]), >27.1 to 29.8 kg/m² (third quartile [Q3]), and >29.8 to 56.3 kg/m² (fourth quartile [Q4]). In BMI Q1, Q2, Q3, and Q4, the frequency of bleeding was 13.8%, 10.1%, 10.8%, and 7.7%, respectively (odds ratio [OR] 1.90, 95% confidence interval [CI] 1.63 to 2.23, p <0.001, for Q1 vs Q4). Multiple logistic regression showed that BMI was independently associated with bleeding (adjusted OR 1.05, 95% CI 1.04 to 1.07, p <0.001, for any bleeding; adjusted OR 1.07, 95% CI 1.04 to 1.09, p <0.001, for access site bleeding; and adjusted OR 1.03, 95% CI 1.01 to 1.05, p = 0.039, for non–access site bleeding with all 3 risk estimates calculated per 1 kg/m² decrease in BMI). Analysis by sex showed an increase in the frequency of bleeding with the decrease in BMI for women and men (p for trend <0.001 for women and men) with no sex-by-BMI interaction (p = 0.90). The Cox proportional hazards model showed that bleeding (adjusted hazard ratio [HR] 2.17, 95% CI 1.67 to 2.82, p <0.001) and BMI (HR 1.03, 95% CI 1.01 to 1.06, p = 0.048, per 1 kg/m² decrease in the BMI) were independently associated with increased risk of 1-year mortality with no bleeding-by-BMI interaction (p = 0.81). In conclusion, BMI is inversely associated with the increased risk of bleeding and mortality after PCI.