Altered mental status (AMS), a common and serious entity in elderly Emergency Department patients, is not well recognized by physicians. Our prospective cohort study evaluated the implementation, by nurses and physicians, of the Ottawa 3DY Scale, a cognitive screening tool. We enrolled 260 patients (60.0% female, mean age 83.7). Screening rates were: overall - 78.3%; physician - 51.8%; and nurse - 64.2%. Interrater reliability was 0.65. Physician and nurse sensitivity was 78.9, 84.6% and specificity was 39.4, 54.2%, respectively, compared with the Mini-Mental State Exam. Patient living situation, educational level, triage location, hospitalization, admission location and 30 day mortality were associated with AMS. Implementation of the Ottawa 3DY Scale increased screening for AMS in elderly Emergency Department patients. It was feasible, sensitive, specific and had good interrater reliability. Use will lead to increased identification of cognitive impairment and ultimately result in improved care and outcomes in this vulnerable patient population.