Evaluated the performance of STOPP (Screening Tool of Older Persons' potentially inappropriate Prescriptions) and Beers' criteria in detecting potentially inappropriate medicines (PIMs) and related adverse drug events (ADEs) in older hospitalized patients in Ireland. STOPP is a systems-defined medicine review tool containing 65 potentially inappropriate prescribing practices in older people, arranged according to relevant physiological systems. Data were prospectively collected from 715 consecutive patients aged 65-94 (median age 77) admitted with acute illness to a university teaching hospital over a 4-month period in 2007. A total of 4,403 medications were prescribed in the cohort, with a median of 6 and a range of 0 to 21. STOPP identified 336 PIMs affecting 247 patients (35%), of whom one-third presented with an associated ADE. Beers' criteria identified 226 PIMs affecting 177 patients (25%), of whom 43 presented with an associated ADE. STOPP-related PIMs contributed to 11.5% of all admissions, while Beers' criteria-related PIMs contributed to 6%. Findings indicate that STOPP criteria are more sensitive in identifying patients coming to harm as a result of inappropriately prescribed medicines than Beers' criteria. (AY) (AgeLine Database, copyright 2009 EBSCO Publishing, Inc., all rights reserved)