OBJECTIVES: Although the Medicare Part D benefit has helped improve prescription medication access and lower out-of-pocket spending for some, variability in drug cost and access restrictions of Part D plans continues to present a challenge for others. The present research sought to examine the reported drug cost and restrictions (Step Therapy (ST), Quantity Limits (QL), Prior Authorization (PA), and Formulary Coverage) associated with each of the 100 (65 generic and 35 brand name) most commonly filled drugs by Medicare beneficiaries under every stand-alone prescription drug plan (PDP) available in California in 2011. METHODS: The list of the top 100 Drugs by total fills under Part D plans in 2008 was retrieved from the Centers for Medicare & Medicaid Services. Each of these drugs was entered into the Medicare Plan Finder Tool (www.medicare.gov). Data found via use of the Plan Finder Tool revealed the full cost, formulary coverage and restriction processes of every examined drug under each of the 2011 California PDPs for which data were available. RESULTS: The difference between the lowest and highest plan reported full cost of each generic (brand) drug from all available PDPs ranged from a low of $3.37 ($5.41) to a high of $134.34 ($106.33). In addition, differences were found between generic and brand medications in terms of drug restrictions (3.08% generic vs. 57.1% brand drugs required ST), (58.46% generic vs. 94.3% brand drugs required QL) and (4.62% generic vs. 31.4% brand drugs required PA) across the PDPs. Finally, 13 (20%) generic and 25 (71.4%) brand-name drugs were not covered on one or more PDP formularies. CONCLUSIONS: Significant differences in medication costs and plan imposed restriction processes exist between the various 2011 California PDPs. Such differences may present additional barriers to Part D plan access and potentially impact health-related outcomes and costs of Medicare beneficiaries.