OBJECTIVES: Adverse drug effects (ADE) and their subsequent injuries lead to increased health resources utilization in older populations. This study aimed to (i) evaluate the types of ADE-related hospitalizations, (ii) analyze the associated costs of hospitalizations and length of stay. METHODS: A retrospective, single-center observational study was conducted at an academic medical center in Singapore.  Records of hospitalizations with diagnoses related to ADEs between January 2006 and December 2013 were identified using the International Classification of Diseases, Ninth and Tenth Revision, Clinical Modification (ICD-9 and 10) codes. Summary statistics were used to report patient demographics, diagnoses, costs of hospitalizations (Singapore dollars, SGD$) and length of hospital stay (LOS) in days. RESULTS: The analysis included a total of 3088 patients aged ≥ 65 years old. The median age was 75 (IQR, 71-81) and majority were female (59.1%). The median cost of hospitalizations was $1014.65 (IQR, $607.65- $2003.40) and the median length of stay was 4 days (IQR, 2-8). The top five causative drug classes for ADE-related hospitalizations were diuretics (31.3%), anticoagulants (21.3%), anti-hypertensive (11.6%), anti-infective (5.6%) and anti-neoplastic (4.8%). Multivariate linear regression showed that anti-infectives are associated with longer LOS and higher total bills compared to the other four ADE-related admissions i.e., 4.8 days longer (p<0.001) and SGD$3734.90 more in cost (p<0.001). This could be due to the various therapeutic monitoring parameters associated with anti-infective use, and a switch of therapy to more expensive alternatives should antibiotic resistance occur. CONCLUSIONS: ADE-related hospitalizations caused significant expenditure and morbidity in older population.  Further efforts are necessary to improve pharmacotherapy and relieve health care payers of preventable treatment costs. Multiple measures to prevent ADE-related hospitalizations such as electronic alerts, improving incidence reporting system, involving pharmacists to aid in prescribing decision and improving nursing administration of medications may potentially address this issue.