Objective: Given the complexity of the Medicare Part D (MPD) prescription drug benefit, many Medicare beneficiaries lack the knowledge and experience to select optimal MPD prescription drug plans. This challenge is exacerbated in low-income and other vulnerable populations. A Cost-Minimization Analysis (CMA) was performed to determine whether and to what extent student pharmacists' interventions reduce out-of-pocket (OOP) prescription drug plan costs for Medicare beneficiaries. Methods: Trained student pharmacists throughout California provided one-on-one MPD prescription drug plan consultations during community outreach events. Cost information for the participant's current and lowest-cost plan for 2008 was obtained by conducting a personalized plan search using the online MPD Plan Finder tool. Results: Twenty-two outreach events were conducted statewide and data were collected from 250 Medicare beneficiaries. The mean ± SD age of the participants was 74.3±9.1 years, and 91 (36.4%) were male. The mean ± SD (range) number of prescription drugs per participant was 5.6±3.9 (0-26). Eighty-three participants (33.2%) had limited or no English proficiency, 82 (32.8%) had less than a high school education, and 102 (40.8%) were enrolled in both Medicare and Medicaid. Data from 95 participants (72 of whom were not enrolled in a MPD drug plan during 2007 and 23 of whom had incomplete data) were necessarily excluded for purposes of the CMA. For the other 155 participants, the median annual OOP costs for continued enrollment in their current MPD prescription drug plan in 2008 were $440.00, compared to $200.00 for the lowest-cost 2008 plan. When cost savings were calculated by individual participant, this equated to a median annual OOP cost savings of $98.00 (22.3%) per participant. Conclusion: Trained student pharmacists can provide community-based interventions that reduce OOP prescription drug plan costs among underserved Medicare populations.