Many medications, particularly sedatives and other drugs with significant side effects, are considered inappropriate for prescribing in elderly patients. However, the existing Beers criteria for appropriateness lack predictive power for adverse drug events. This prospective cohort study reports on the validation of the STOPP criteria, a novel list of medications considered inappropriate for elderly patients. Patients who received medications considered inappropriate by STOPP had a nearly two-fold increased odds of an adverse drug event during hospitalization, while the Beers criteria failed to predict medication errors. Given the recognized limitations of the Beers criteria, the STOPP criteria likely represent a superior method of identifying dangerous medications in geriatric patients.