A formal user evaluation of an integrated medical workstation for support of clinical data analysis is described. Twenty-six users participated in an assessment study that consisted of a self-instruction course, followed by an experiment in which six clinical data analysis problems had to be solved, and the assessment was concluded with an evaluation form. To facilitate an objective and quantitative assessment, the time spent to the course and to the problems, as well as completeness, correctness, number of solving attempts and persistence were measured. Not all problems were solved by all participants. From an analysis of the measurements, the following conclusions were drawn. (1) Clinicians correctly solved about 69% of all problems tackled. However, they skipped 33% of the problems. (2) Non-clinicians correctly solved 87% of the tackled problems and skipped only 10%. (3) The performance of users not experienced in clinical data analysis was raised to the level of those with clinical data analysis experience. (4) An inventory which can be used to direct future developments was made of the errors of interaction. This assessment study has contributed to gaining insight into the conceptual problems and practical bottlenecks clinicians have with clinical data analysis.