Case report forms (CRF) specify data definitions and encodings for data to be collected in clinical trials. To enable exchange of data definitions and in this way to avoid creation of variants of CRF for similar study designs, the Medical Data Model portal (MDM) has been developed since 2011. This work aims at studying the usability of the MDM portal. We identify issues that hamper its adoption by researchers in order to derive measurements for improving it. We selected relevant tools (e.g. Nibbler, Hotjar, SUPR-Q) for usability testing and generated a structured test protocol. More specifically, the portal was assessed by means of a static analysis, user analysis (n=10), a usability test (n=10) and statistical evaluations. Regarding accessibility and technology, the static code analysis resulted in high scores. Presentation of information and functions as well as interaction with the portal still has to be improved: The results show that only limited functions of the webpage are used regularly and some user navigation errors occur due to the portal’s design. In total, six major problems were identified which will be addressed in future. A continuous evaluation using the same structured test protocol allows to continuously measure the website quality, to compare it after changes have been implemented and in this way, to realise a continuous improvement. The effort for a repeated evaluation of the same evaluation with 10 persons is estimated with 10 hours.