Inappropriate medication use is a major patient safety concern, especially for the elderly population. Using explicit criteria, prior studies have found that 23.5% and 17.5% of the US community-dwelling elderly population used at least 1 of 20 potentially inappropriate medications in 1987 and 1992, respectively. To determine the prevalence of potentially inappropriate medication use in community-dwelling elderly persons in 1996, to assess trends over 10 years, categorize inappropriate medication use according to explicit criteria, and to examine risk factors for inappropriate medication use. Respondents aged 65 years or older (n = 2455) to the 1996 Medical Expenditure Panel Survey, a nationally representative survey of the US noninstitutionalized population were included. A 7-member expert panel was convened to categorize inappropriate medications. Prevalence of use of 33 potentially inappropriate medications. In 1996, 21.3% (95% confidence interval [CI], 19.5%-23.1%) of community-dwelling elderly patients in the United States received at least 1 of 33 potentially inappropriate medications. Using the expert panel's classifications, about 2.6% of elderly patients (95% CI, 2.0%-3.2%) used at least 1 of the 11 medications that should always be avoided by elderly patients; 9.1% (95% CI, 7.9%-10.3%) used at least 1 of the 8 that would rarely be appropriate; and 13.3% (95% CI, 11.7%-14.9%) used at least 1 of the 14 medications that have some indications but are often misused. Use of some inappropriate medications declined between 1987 and 1996. Persons with poor health and more prescriptions had a significantly higher risk of inappropriate medication use. Overall inappropriate medication use in elderly patients remains a serious problem. Despite challenges in using explicit criteria for assessing inappropriate medications for elderly patients, such criteria can be applied to population-based surveys to identify opportunities to improve quality of care and patient safety. Enhancements of existing data sources to include dosage, duration, and indication may augment national improvement and monitoring efforts.