The overall objective of the eu-ADR project is the design, development,and validation of a computerised system that exploits data from electronichealth records and biomedical databases for the early detection ofadverse drug reactions. Eight different databases, containing healthrecords of more than 30 million European citizens, are involved inthe project. Unique queries cannot be performed across differentdatabases because of their heterogeneity: Medical record and Claimsdatabases, four different terminologies for coding diagnoses, andtwo languages for the information described in free text. The aimof our study was to provide database owners with a common basis forthe construction of their queries. Using the UMLS, we provided alist of medical concepts, with their corresponding terms and codesin the four terminologies, which should be considered to retrievethe relevant information for the events of interest from the databases.