OBJECTIVES: To investigate the impact of Medicare Part D on prescription utilization, health services utilization, and health care expenditures in the general Medicare population METHODS: A retrospective analysis of Medicare beneficiaries (N=32,228) was conducted using the Medical Expenditure Panel Survey 2002 to 2009 data. Multivariable quantile regression was used to estimate the following outcomes at the 25th, 50th, 75th, and 90th percentiles, adjusting for socio-demographic characteristics: 1) number of prescription fills; 2) out-of-pocket (OOP) drug expenditures; 3) total drug expenditures; 4) OOP health care expenditures; 5) total health care expenditures; 6) number of hospitalizations; and 7) number of emergency department (ED) visits between the pre-Part D (2002-2005) and post-Part D (2006-2009) periods. All expenditures were inflation-adjusted to 2009 dollars. RESULTS: In the general Medicare population, Part D was associated with decreases in OOP drug expenditures (-25.7% to -33.6%; p<0.0001) and OOP health care expenditures (-22.1% to -24.3%; p<0.0001) across all percentiles. Part D was associated with increases in the number of prescription fills across all percentiles (5.8% to 8.4%; p<0.0001) but only at the 75th and 90th percentiles for increases in total drug expenditures (75th percentile: 5.5%; 90th percentile: 10.2%; p<0.0001). Part D was not associated with changes in total health care expenditures, hospitalizations, or ED visits in the general Medicare population. CONCLUSIONS: Part D resulted in increases in medication utilization and reductions in OOP drug and OOP health care expenditures among Medicare beneficiaries, but was not associated with differences in total health care spending, hospitalizations, or ED visits.