Background:The impact of body mass index (BMI) on the clinical outcomes after percutaneous coronary intervention (PCI) in patients ≥75 years old remained unclear.Methods:A total of 1098 elderly patients undergoing PCI with stent implantation were recruited.Patients were divided into four groups by the value of BMI:Underweight (＜20.0 kg/m2),normal weight (20.0-24.9 kg/m2),overweight (25.0-29.9 kg/m2) and obese (≥30.0 kg/m2).Major clinical outcomes after PCI were compared between the groups.The primary endpoint was defined as in-hospital major adverse cardiovascular events (MACEs),which included death,myocardial infarction (MI) and target vessel revascularization.The secondary endpoint was defined as 1 year death.Logistic regression analysis was performed to adjust for the potential confounders.Results:Totally,1077 elderly patients with available BMIs were included in the analysis.Patients of underweight,normal weight,overweight and obese accounted for 5.6％,45.4％,41.5％ and 7.5％ of the population,respectively.Underweight patients were more likely to attract ST-segment elevation MI,and get accompanied with anemia or renal dysfunction.Meanwhile,they were less likely to achieve thrombolysis in MI 3 grade flow after PCI,and receive beta-blocker,angiotensin converting enzyme inhibitor or angiotensin receptor blocker after discharge.In underweight,normal weight,overweight and obese patients,in-hospital MACE were 1.7％,2.7％,3.8％,and 3.7％ respectively (P =0.68),and 1 year mortality rates were 5.0％,3.9％,5.1％ and 3.7％ (P =0.80),without significant difference between the groups.Multivariate regression analysis showed that the value of BMI was not associated with in-hospital MACE in patients at 75 years old.Conclusions:The BMI obese paradox was not found in patients ≥75 years old.It was suggested that BMI may not be a sensitive predictor of adverse cardiovascular events in elderly patients.