Adverse drug events (ADEs) are an increasingly relevant issue for healthcare systems as they are associated with poorer health outcomes and avoidable misuse of resources. The rates of ADEs are higher in the elderly population, as many older patients have comorbidities, multiple drug prescriptions and deteriorated physical and cognitive functioning. The occurrence of ADEs can lead to a perceived lack of therapy efficacy and further underuse or suboptimal adherence in elderly people, with detrimental clinical outcomes. The present article systematically reviews the studies evaluating the economic impact of ADEs occurring as consequence of poor therapy adherence, inappropriate drug use, underuse of effective treatments and poor adherence, medication errors, drug-drug and drug-disease interactions.A Medline systematic literature review of studies evaluating the economic consequences of inappropriate drug prescribing, lack of adherence and compliance, ADEs in older people was performed. English-language articles were screened through a three-step approach (title review, abstract review, full article review) to select pertinent studies quantitatively evaluating costs. We systematically reviewed evidence from767 articles. After title, abstract and full text review, 21 articles were found to measure economic implications ofADEs, inappropriate drug prescribing and poor adherence in elderly patients. Studies suggested that the economic impact of these undesired effects is substantial: hospital costs were the main cost driver, with a relevant part of them being preventable (consequences of inappropriate prescribing). Healthcare costs for unused drug wastage and destruction were also surprisingly high.Although economic evidence in elderly patients is still limited, all studies seemed to confirm that the financial burden due to pharmacological treatment issues is relevant in elderly people. Including economic effects of adverse events in pharmacoeconomic analysis would be beneficial to improve the reliability of results. Preliminary evidence suggests that programmes aimed at comprehensively assessing geriatric conditions, detecting 'high-risk' prescriptions and training patients to comply with prescribed therapies could be costeffective measures to reduce the burden of ADEs.