Introduction: STOPP (Screening Tool of Older Persons' potentially inappropriate Prescriptions) is a new, systems-defined medicine review tool. We compared the performance of STOPP to that of established Beers' criteria in detecting potentially inappropriate medicines (PIMs) and related adverse drug events (ADEs) in older patients presenting for hospital admission.Methods: we prospectively studied 715 consecutive acute admissions to a university teaching hospital. Diagnoses, reason for admission and concurrent medications were recorded. STOPP and Beers' criteria were applied. PIMs with clear causal connection or contribution to the principal reason for admission were determined.Results: median patient age (interquartile range) was 77 (72-82) years. Median number of prescription medicines was 6 (range 0-21). STOPP identified 336 PIMs affecting 247 patients (35%), of whom one-third (n = 82) 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. Beers' criteria-related PIMs contributed to significantly fewer admissions (6%).Conclusion: STOPP criteria identified a significantly higher proportion of patients requiring hospitalisation as a result of PIM-related adverse events than Beers' criteria. This finding has significant implications for hospital geriatric practice.