Electronic Medical Records should capture structured clinical information to support programs used at the point of clinical care. For that, numerous terminological systems have been developed, providing structure and leading to interoperability. Interface terminologies are regarded the most important and are designed to translate clinicians’ own natural terms into a more structured representation of concepts needed by the applications. An interface terminology, i.e. DICE (Diagnoses for Intensive Care Evaluation), was developed for the Intensive Care to uniform and standardize diagnostic information. We evaluated the usability of this new interface terminology by testing the performance and learn-ability. Literature searches were done to gain information and the results were used to design the usability evaluation study of DICE. A case study was performed by using the Think Aloud method, SUS questionnaire and measuring the Time on Task. The usability evaluation of DICE has provided us with useful information. The research and results are useful for other researchers intending to test the usability of interface terminologies.