OBJECTIVES: 1) Isolate trends in the prevalence of inappropriate prescribing among elderly Medicare beneficiaries; 2) determine which inappropriate medicines are the most commonly prescribed; and 3) identify the relationship between inappropriate prescribing and drug coverage. METHODS: Using 10 years of prescribed medicine event (PME) data from the Cost and Use component of the Medicare Beneficiary Survey (MCBS) 1992-2001, we estimated the weighted prevalence of inappropriate prescribing, based on Beer's Criteria, among elderly beneficiaries. The MCBS is a longitudinal survey; therefore participant may contribute multiple years of PME data. These data were stratified by year and chi-squared tests on differences in inappropriate prescribing by drug coverage were conducted to address the hypothesis that Medicare Part D may increase the prevalence of inappropriate prescribing by reducing economic barriers to access. RESULTS: Among the 94,372 person-years of data, 31.8% reported inappropriate prescribing. From 1992 to 2001, the weighted prevalence of inappropriate prescribing ranged from 30.2% in 2001 to 33.8% in 1993. The three most common inappropriate medications were propoxyphene (7.0%), naproxen (3.6%), and amitriptyline (3.1%), but their prevalence varied greatly by year. Drug coverage was positively associated with inappropriate prescribing in each year. CONCLUSION: The findings suggest that inappropriate prescribing remains prevalent in geriatric care. The fact that there was no significant decline in inappropriate prescribing highlights the importance of adapting more effective policy measures to improve prescribing patterns in geriatric patients. The findings also suggest that drug coverage was associated with higher prevalence of inappropriate prescribing probably caused by increase access to care.