Background: Each year, Medicare beneficiaries can receive their prescription drug coverage from any one of a number of Part D plans. Failure to evaluate Part D plan offerings annually can result in unnecessary out-of-pocket (OOP) costs. Objectives: This study examined the potential OOP cost savings through annual Part D plan reexamination for beneficiaries in a stand-alone prescription drug plan (PDP) as a function of subsidy status and plan offerings in California from 2008 to 2013. Study Design: Six-year longitudinal cross-sectional study. Methods: Fifty-nine community outreach events were held throughout central and northern California during the Medicare open enrollment periods each year from 2007 to 2012. In total, 2262 beneficiaries were assisted, of whom 1476 (68%) had a PDP. During each intervention, beneficiary sociodemographic characteristics (eg, subsidy status) and cost data for their current PDP and the lowest cost PDP in the upcoming year were recorded from the Medicare website (www.medicare.gov). Results: On average, only 20% of beneficiaries would have been enrolled in the lowest cost plan in the upcoming year had they remained in their current plan. The average potential annual cost savings from switching to the lowest cost PDP in the upcoming year during the study period was $728. Subsidy recipients were more likely to be in the lowest cost plan in the upcoming year. Conclusions: Because of the fluctuation of Part D plan offerings each year, annual Part D plan reexamination has been, and remains, essential in ensuring that beneficiaries optimize their prescription medication coverage and minimize OOP costs.