OBJECTIVE--To examine the amount of inappropriate drug prescribing for Americans aged 65 years or older living in the community. DESIGN--Cross-sectional survey of a national probability sample of older adults. SETTING--The 1987 National Medical Expenditure Survey, a national probability sample of the US civilian noninstitutionalized population, with oversampling of some population groups, including the elderly. SUBJECTS--The 6171 people aged 65 years or older in the National Medical Expenditure Survey sample, using appropriate weighting procedures to produce national estimates. MAIN OUTCOME MEASURES--Incidence of prescribing 20 potentially inappropriate drugs, using explicit criteria previously developed by 13 United States and Canadian geriatrics experts through a modified Delphi consensus technique. Three cardiovascular drugs identified as potentially inappropriate were analyzed separately since they may be considered appropriate for some noninstitutionalized elderly patients. RESULTS--A total of 23.5% (95% confidence interval [CI], 22.4% to 24.6%) of people aged 65 years or older living in the community, or 6.64 million Americans (95% CI, 6.28 million to 7.00 million), received at least one of the 20 contraindicated drugs. While 79.6% (95% CI, 77.2% to 82.0%) of people receiving potentially inappropriate medications received only one such drug, 20.4% received two or more. The most commonly prescribed of these drugs were dipyridamole, propoxyphene, amitriptyline, chlorpropamide, diazepam, indomethacin, and chlordiazepoxide, each used by at least half a million people aged 65 years or older. Including the three controversial cardiovascular agents (propranolol, methyldopa, and reserpine) in the list of contraindicated drugs increased the incidence of probably inappropriate medication use to 32% (95% CI, 30.7% to 33.3%), or 9.04 million people (95% CI, 8.64 million to 9.44 million). CONCLUSION--Physicians prescribe potentially inappropriate medications for nearly a quarter of all older people living in the community, placing them at risk of drug adverse effects such as cognitive impairment and sedation. Although most previous strategies for improving drug prescribing for the elderly have focused on nursing homes, broader educational and regulatory initiatives are needed.