Background: In late 2015, the American Geriatric Society released the updated Beers Criteria for potentially inappropriate medication (PIM) use in older adults. Currently, ~84% of 55 million US Medicare beneficiaries are 65 years of age or older. We utilized the updated Beers Criteria to examine the prevalence of PIM use by older Medicare beneficiaries. methods: We held 13 Mobile Clinics in northern/central California during fall 2015. Beneficiaries at each clinic site were provided a myriad of health services including Medication Therapy Management (MTM). Each MTM intervention included a comprehensive review of the beneficiary's medication regimen. The intervention was conducted via a structured interview during which drug, disease state, and sociodemographic data were collected. Each beneficiary's current drug therapy was examined against the 2015 Beers Criteria. results: MTM services were provided to 860 beneficiaries; 703 were 65 years of age or older and taking at least one medication. This latter group comprised the study sample. In total, 328 (46.7%) beneficiaries were taking at least one PIM. Therapeutic categories in which the highest number of PIMs were found included: Benzodiazepines (n=87[(26.5%]), Non-cyclooxygenase-selective oral NSAIDs (n=45[13.7%]), and Nonbenzodiazepine/Benzodiazepine receptor agonist hypnotics (n=37[11.3%]). The prevalence of PIMs significantly varied as a function of race, subsidy status, and presence of certain disease states. conclusion: In light of the updated and more inclusive Beers Criteria, prescribers, pharmacists and other healthcare professionals should closely examine the medication regimen of older adults; doing so may improve medication selection, reduce adverse drug events, and improve a patient's quality-of-life.