Background Older individuals often suffer from multiple co-morbidities and are particularly vulnerable to potentially inappropriate prescribing (PIP). One method of defining instances of PIP is to use validated, evidence-based, explicit criteria. Two sets of criteria have gained international recognition: the Screening Tool of Older Persons' potentially inappropriate Prescriptions (STOPP) and Beers' criteria.Objectives The study aims were to (1) determine the prevalence of PIP in older residents residing in long-term care (LTC) facilities in the greater Cork region of Ireland using these tools; (2) assess the applicability of the STOPP and Beers' criteria and compare the prevalence of PIP determined by each set of criteria; and (3) investigate the association between the occurrence of PIP determined by both tools and the number of medications prescribed, age, sex and Charlson Comorbidity Index (CCI) score.Method All 15 publically funded LTC facilities in the greater Cork region of Ireland were approached, and 14 agreed to participate. Residents aged >= 65 years were included. Exclusion criteria included terminally ill residents or residents receiving respite care. The prevalence of PIP was determined by applying the STOPP and Beers' criteria to each resident's medication profile. Two multivariate logistic regression models examined the association between the occurrence of PIP as determined by STOPP criteria and by Beers' criteria and the number of drugs prescribed, age, sex and CCI score.Results The sample population in this study included 732 residents from 14 LTC facilities; the median age was 85 years (interquartile range [IQR] 79-89) and 514 residents (70.2 %) were female. The total number of medications prescribed was 8,325 (median 11, IQR 9-14; range 2-25). At least one instance of PIP was experienced by approximately 70 % of patients when evaluated using the STOPP criteria, while the corresponding figure was 53.4 % using Beers' criteria. STOPP identified 1,280 instances of PIP relating to 1,140 potentially inappropriate medications (PIMs), while Beers' criteria identified 833 instances of PIP relating to 704 PIMs. Multivariate regression analysis, taking age, sex, disease burden and number of medications into consideration, showed a significant positive association between the number of medications and PIP as defined by STOPP (odds ratio [OR] 1.295, 95% CI 1.223, 1.372; p < 0.001) and Beers' criteria (OR 1.263, 95% CI 1.201, 1.327; p < 0.001). Significant negative associations were also found between CCI score and the occurrence of PIP as defined by STOPP (OR 0.857, 95% CI 0.760, 0.966; p < 0.05) and the occurrence of PIP as defined by the Beers criteria (OR 0.843, 95% CI 0.754, 0.943; p < 0.05).Conclusion In this LTC population, STOPP criteria identified a higher percentage of PIMs and a higher prevalence of PIP than the Beers criteria. The higher prevalence of PIP determined using the STOPP criteria is of uncertain relevance, but may be because STOPP was designed and validated for use in an Irish setting.