Abstract Background Unequivocal identification of patients is a precondition for a safe medical journey through different information systems (ISs) and software applications that are communicating and exchanging interoperable data. A master patient index (MPI) can facilitate this task. Being a repository of patient identity traits, a MPI allows an accurate surveillance of the patients’ “medical identities”. Up to 2014, the Grand Duchy of Luxembourg did not possess a MPI. Here, we describe our experience in the establishment of a national MPI for the Grand Duchy of Luxembourg. Methods The different steps that were used to establish the MPI system are described. Firstly, through the identification of the suitable application and, secondly, through the implementation of the MPI to the eHealth national platform and its connection to the national health care system. In parallel to the first two phases, the identity management policies were defined and implemented. Results Since 2014, when the MPI was integrated to the eHealth platform, we observed a continuous increase of identity profiles. At the latest update (31 December 2018), 2.418.336 identity profiles have been counted, including almost the totality of Luxembourgish residents (95.2%) as well as all the cross-border workers that are affiliated to the Luxembourgish social security system. An analysis of the identification domains connected to the platform highlighted a yearly increase in the usage rate of the identities by external applications (currently representing 70%). The evaluation of the quality of information contained in each identity profile showed low rejection rates (0.2%), indicating a high quality and a good level of completeness in regards to the required identity traits. Conclusions This paper presents the current state of patient identity management in Luxembourg and discusses how this synergistically supports the functioning of the national electronic health record (EHR) known as DSP (from the French Dossier de Soins Partagé) and the ...