OBJECTIVES: Erythropoiesis-Stimulating Agents (ESAs) are mainly administered in physician’s offices and covered under Medicare Part B. Since the implementation of Medicare Part D, ESAs could also be covered under Part D. Total costs associated with ESA use are lower when covered under Part D than Part B. The objective of the study was to explore factors associated with ESA use under Medicare Part D. METHODS: This study was a pooled cross-sectional study of the Medicare Current Beneficiary Survey from 2006 to 2011. The study sample was selected from ESA users, defined as having at least one Part B or Part D claim indicating ESA use. Individuals enrolled in health maintenance organization plans were excluded from the study. A logistic regression model was used to identify predictors of ESA use under Medicare Part D. RESULTS: The study identified 754 ESA users. Among them, 148 (19.63%) had any Part D claims and 606 (80.37%) had only Part B claims. Predictors of ESA use under Medicare Part D included: had less number of Medicare claims (1-5 claims [OR: 22.20, 95% CI: 6.76-72.90] and 6-15 claims [OR: 4.62, 95% CI: 1.43-14.99]), had higher education level (some college [OR: 2.25, 95% CI: 1.05-4.85] and college graduate [OR: 3.12, 95% CI: 1.34-7.28]), lived in metropolitan areas (OR: 2.30, 95% CI: 1.18-4.48), lived in Northeast (OR: 3.01, 95% CI: 1.41-6.45), were eligible for Medicare care because of age (OR: 6.99, 95% CI: 3.06-15.93), had fair or poor health (OR: 2.11, 95% CI: 1.18-3.76), and had low-income subsidy (OR: 2.53, 95% CI: 1.25-5.13). CONCLUSIONS: The society, healthcare providers, and patients should be aware of factors associated with ESA use under Medicare Part D. Appropriate actions should be taken to improve the utilization of ESAs under Medicare Part D to generate cost-savings in the society.