The fact that resources for health care are limited has been found as a rationale for the development of pharmacoeconomics. Pharmacoeconomic analysis identifies, measures and compares the costs and the economic, clinical and humanistic outcomes of diseases, drug therapies and programmes directed to these diseases. As health care expenditures have escalated over the past decades, the number of its applications has increased. Taking into consideration outcome and economic issues and establishing their mutual relationship helps proper resource allocation. In the case of some effective and toxic drugs therapeutic drug monitoring has been proven to allow obtaining the desired clinical effects safely and thus to improve outcome. However, it requires the presence of clinical pharmacology or clinical pharmacy service within a hospital, which in turn is associated with some additional costs. This review sums up the results of pharmacoeconomic studies relevant to the use of therapeutic drug monitoring in case of the medicines for which it has been commonly performed so far.