Purpose: Medicare Part D provided 3.4 million American seniors with prescription drug insurance. It may also have had an unintended effect on pharmacy viability. This study compares trends in the number of pharmacies and rate of pharmacy closures before and after the implementation of Medicare Part D. Methods: This retrospective observational study used data from National Council for Prescription Drug Programs (NCPDP) to track retail pharmacy closures and counts between January 2004 and January 2009. Pharmacies were classified by ownership (chain or independent), location (urban or rural), and whether they were the only pharmacy in a community. Autoregressive Integrated Moving Average (ARIMA) models were used to examine trends in pharmacy counts and closures. Findings: The number of independent and rural pharmacies decreased significantly after the implementation of Medicare Part D. The number of communities that saw their only pharmacy close also increased. Conclusions: Unintended consequences of Medicare Part D may serve to reduce patient access to pharmacy services in opposition to the stated goals of the program.