Introduction: Adverse drug events (ADEs) are associated with inappropriate prescribing (IP) and result in increased morbidity, mortality and resource utilisation. We used Beers Criteria to determine the three-month prevalence of IP in a non-selected community-dwelling population of acutely ill older people requiring hospitalisation.Methods: A prospective, observational study of 597 consecutive acute admissions was performed. Diagnoses and concurrent medications were recorded before hospital physician intervention, and Beers Criteria applied.Results: Mean patient age (SD) was 77 (7) years. Median number of medications was 5, range 013. IP occurred in 32% of patients (n = 191), with 24%, 6% and 2% taking 1, 2 and 3 inappropriate medications respectively. Patients taking 5 medications were 3.3 times more likely to receive an inappropriate medication than those taking <= 5 medications (OR 3.34: 95%, CI 2.374.79; P < 0.001). Forty-nine per cent of patients with inappropriate prescriptions were admitted with adverse effects of the inappropriate medications. Sixteen per cent of all admissions were associated with such adverse effects.Conclusion: IP is highly prevalent in acutely ill older patients and is associated with polypharmacy and hospitalisation. However, Beers Criteria cannot be used as a gold standard as they do not comprehensively address all aspects of IP in older people.