This study updates and expands explicit criteria defining potentially inappropriate medication use by the elderly. Additional goals were to address whether adverse outcomes were likely to be clinically severe and to incorporate clinical information on diagnoses when available. These criteria are meant to serve epidemiological studies, drug utilization review systems, health care providers, and educational efforts. Consensus from a panel of 6 nationally recognized experts on the appropriate use of medication in the elderly was sought. The expert panel agreed on the validity of 28 criteria describing the potentially inappropriate use of medication by general populations of the elderly as well as 35 criteria defining potentially inappropriate medication use in older persons known to have any of 15 common medical conditions. Updated, expanded, and more generally applicable criteria are now available to help identify inappropriate use of medications in elderly populations. These criteria define medications that should generally be avoided in the ambulatory elderly, doses or frequencies of administrations that should generally not be exceeded, and medications that should be avoided in older persons known to have any of several common conditions.