Abstract Background Risk stratification of older patients in the emergency department (ED) is seen as a promising and efficient solution for handling the increase in demand for geriatric emergency medicine. Previously, the predictive validity of commonly used tools for risk stratification, such as the identification of seniors at risk (ISAR), have found only limited evidence in German geriatric patient samples. Given that the adverse outcomes in question, such as rehospitalization, nursing home admission and mortality, are substantially associated with cognitive impairment, the potential of the short portable mental status questionnaire (SPMSQ) as a tool for risk stratification of older ED patients was investigated. Objective To estimate the predictive validity of the SPMSQ for a composite endpoint of adverse events (e.g. rehospitalization, nursing home admission and mortality). Method This was a prospective cohort study with 260 patients aged 70 years and above, recruited in a cardiology ED. Patients with a likely life-expectancy below 24 h were excluded. Follow-up examinations were conducted at 1, 3, 6 and 12 month(s) after recruitment. Results The SPMSQ was found to be a significant predictor of adverse outcomes not at 1 month (area under the curve, AUC 0.55, 95% confidence interval, CI 0.46–0.63) but at 3 months (AUC 0.61, 95% CI 0.54–0.68), 6 months (AUC 0.63, 95% CI 0.56–0.70) and 12 months (AUC 0.63, 95% CI 0.56–0.70) after initial contact. Conclusion For longer periods of observation the SPMSQ can be a predictor of a composite endpoint of adverse outcomes even when controlled for a range of confounders. Its characteristics, specifically the low sensitivity, make it unsuitable as an accurate risk stratification tool on its own.