OBJECTIVES: Pharmacogenetics holds the promise of preventing adverse drug events (ADRs) but the diffusion of these diagnostic testsis still limited. Assessing cost-effectiveness of pharmacogenetic interventions, a key to successful clinical implementation, requires access to data on ADRs and related costs which are not readily available. This study focuses on ADRs induced by azathioprine (AZA) treatment in Rheumatoid Arthritis and Inflammatory Bowel Disease patients, for whom there is a recognized association between the occurrence of severe neutropenia and the diminished activity of TPMT. The study aims at evaluating the availability and quality of cost data related to: (i) the treatment and management of ADRs induced by AZA and (ii) the use of TPMT diagnostic kits in an average laboratory. The overall objective is to review the possibility of building a cost-effectiveness model on European data. METHODS: A literature review was conducted on PubMED and Embase databases.. The clinical path for the management of AZA-induced ADRs was elaborated with an international panel of gastroenterologists/rheumatologists. RESULTS: Very few studies describe costs of treating ADRs induced by AZA. When present, costs are rarely collected empirically but derived from national tariff databases or from a single healthcare organization, resulting in a large variability. Reported costs are only direct, disregarding productivity losses, while ADRs often require hospitalization. Direct annual costs for ADRs range from € 476 to € 5505. It is equally difficult to identify solid data on the costs o TPMT diagnostic tests in an average European laboratory, with estimates between 70€ and 130€. CONCLUSION: Cost-effectiveness data might influence the degree of confidence of healthcare organizations in adopting new technologies. Published economic studies that evaluate TPMT diagnostic tests and the costs they might prevent are still rather weak. Prospective economic studies, that systematically include the evaluation of ADR costs, are urgently needed.