Background: The identification of patients at high risk for adverse outcomes [death, unplanned readmission to emergency department (ED)/hospital, functional decline] plays an important role in emergency medicine. The Identification of Seniors at Risk (ISAR) instrument is one of the most commonly used and best-validated screening tools. As to the authors' knowledge so far there are no data on any screening tool for the identification of older patients at risk for a negative outcome in Germany. Objectives: To evaluate the validity of the ISAR screening tool in a German ED. Design: This was a prospective single-center observational cohort study in an ED of an urban university-affiliated hospital. Participants were 520 patients aged ≥75 years consecutively admitted to the ED. Measurements: The German version of the ISAR screening tool was administered directly after triage of the patients. Follow-up telephone interviews to assess outcome variables were conducted 28 and 180 days after the index visit in the ED. The primary end point was death from any cause or hospitalization or recurrent ED visit or change of residency into a long-term care facility on day 28 after the index ED visit. Results: The mean age ± SD was 82.8 ± 5.0 years. According to ISAR, 425 patients (81.7%) scored ≥2 points, and 315 patients (60.5%) scored ≥3 points. The combined primary end point was observed in 250 of 520 patients (48.1%) on day 28 and in 260 patients (50.0%) on day 180. Using a continuous ISAR score the area under the curve on day 28 was 0.621 (95% confidence interval, CI 0.573-0.669) and 0.661 (95% CI 0.615-0.708) on day 180, respectively. Conclusion: The German version of the ISAR screening tool acceptably identified elderly patients in the ED with an increased risk of a negative outcome. Using the cutoff ≥3 points instead of ≥2 points yielded better overall results.