Terminology is significant for professional communication and ipso facto for translation quality assurance (QA). To deliver a translation of high quality, it is crucial to have all new terms that occur in professional discourse collected, stored and managed properly by means of terminology databases (TDBs). In this paper I will try to define ‘quality’ in relation to TDBs and to determine the methodology and criteria that need to be considered by evaluating a TDB in the context of its reliability.