OBJECTIVES: Conventional (on-pump) coronary artery bypass grafting (CABG) is a surgical procedure used to restore blood flow to the cardiac muscle in patients with coronary artery disease.  Recently, some have suggested that an off-pump CABG procedure has lesser post-operative morbidity and mortality.  Few studies to corroborate this finding have been conducted in the elderly population. The purpose of this study was to compare outcomes associated with on-pump and off-pump CABG among Medicare beneficiaries.   METHODS: A retrospective cohort study design was used to analyze the 5% national sample of Medicare claims data.  Elderly patients (≥65 years) who underwent CABG from July 1, 2006 to June 30, 2008 were identified using ICD-9-CM codes.  Outcomes were assessed (using ICD-9-CM codes) following CABG surgery to December 31, 2008.  Outcomes included acute myocardial infarction (AMI), revascularization such as percutaneous coronary intervention (PCI), stroke, in-hospital and all-cause mortality.  Propensity scores were calculated to predict the likelihood of each individual receiving on-pump versus off-pump CABG surgery based on patient demographics and comorbidities (identified from January 1to June 30, 2006) which were then used to match (1:1) patients in the two groups.  Conditional logistic regression was used to compare the outcomes associated with the two procedures.  RESULTS: 2,760 patients (1,380 in each group) met the inclusion criteria.  Patients who underwent on-pump CABG had lower odds of in-hospital mortality (OR: 0.57; 95% CI: 0.39 – 0.83) and all-cause mortality (OR: 0.69; 95% CI: 0.56 – 0.85) as compared to off-pump CABG patients.  The procedures were found to be comparable in terms of clinical outcomes including AMI, PCI and stroke.   CONCLUSIONS: This study found that in-hospital and all-cause mortality associated with on-pump CABG was lower than off-pump CABG.  Further clinical trials need to be conducted to compare the safety of on-pump versus off-pump CABG among elderly patients.