Information Visualization (InfoVis) techniques can offer a valuable contribution for the examination of medical data. We successfully developed an InfoVis application – Gravi – for the analysis of questionnaire data stemming from the therapy of anorectic young women. During the development process, we carefully evaluated Gravi in several stages. In this paper, we describe selected results from the usability evaluation, especially results from qualitative studies. The results indicate that Gravi is easy to use and intuitive. The subjects of the two studies described here especially liked the presentation of timeoriented data and the interactivity of the system. In the second study, we also found indication that Gravi can be used in other areas than the one it was developed for.