OBJECTIVES:  Most Thai elderly had multiple diseases that high-risk medications (HRM) were subsequently used. In this study, HRM was defined as any medications which posed more risks than benefits in elderly, and those might be replaced by other medications. The study aimed to obtain the prevalence of HRM, pharmaceutical expenditures and patient’s factors associated with HRM. METHODS: A 65-year-old inpatient and older, who had at least an admission during the fiscal year 2013 at the study hospital, was systematically sampled. All inclusive 393 elderly inpatients were selected. A country-specific HRM screening tool developed by Ploylueamsang and colleagues was applied in this cross-sectional study. Logistic regression was to analyze the association between patient’s factors and HRM. RESULTS:  Of all 393 elderly inpatients, 74.3 per cent [292/393] received at least one HRM. Moderate to severe HRM was given by one fifth of all elderly inpatients. Moreover, 7.6 per cent [30/393] of those patients had experienced the use of all mild, moderate, and severe HRM during the study period. The pecentage of HRM expenses to overall medication expenses across all study inpatients was 3.5% [1,030/29,501, monetary unit: US$]. However, the difference of overall medication expenditures between HRM and non-HRM was insignificantly observed (p>0.05). Gastrointestinal drugs accounted for by a half of all HRM expenditures. Patient who had more frequent hospital visits was a likelihood of given HRM (>2 vs. 1-2: OR=5.440, 95%CI=1.249-23.690, p=0.024). The more number of medications was given, the higher HRM was observed. (6-10 vs. 1-2: OR=2.414, 95%CI=1.150-5.068, p=0.020; >10 vs. 1-2: OR=5.152, 95% CI=2.315-11.466, p<0.01). CONCLUSIONS:  A prospective population-based study of HRM and its adverse event should be further conducted in Thailand. Ultimately, the safety and vigilance of HRM given among the elderly inpatients, in particular those who used polypharmacy and had more frequent hospitalizations should be monitored by hospital pharmacists.