BACKGROUND: Health-related Quality of Life (HRQL) of patients is increasingly being used as an endpoint in multinational studies. In this era of international collaboration, there is a critical need for improved interpretation of HRQL studies and the confirmation of conceptual equivalence of linguistically adapted HRQL instruments used in multinational studies. In order to facilitate these two objectives, Mapi Research Institute has launched the development of IQOD. OBJECTIVES: The primary objective of the IQOD project is the development of an international database that will contain HRQL, socio-demographic, and clinical data from multinational HRQL studies. Once this database is developed the following objectives can be realised: (1) Development of reference values to facilitate interpretation of scale scores and making it possible to estimate the relative burden of various medical and psychological conditions across populations and across disease severities; (2) Evaluation of the conceptual equivalence of linguistically adapted HRQL instruments used in multinational studies; (3) Development of item banking. METHODS: During the initial phase of this project, data will be obtained from sponsors of international studies in which linguistically valid HRQL questionnaires, provided by Mapi Research Institute, were administered. There are 13 instruments included in the initial phase of this project. The first step of the initial phase is the development of reference values for the Women's Health Questionnaire (WHQ) and the Minnesota Living with Heart Failure Questionnaire (MLHF). RESULTS: Results of the initial phase will be presented upon completion of analysis.