BACKGROUND: In an earlier study, our research group presented an alternative approach to measuring knowledge about mental disorders by constructing a structure-based expert model of the ICD-10 mental disorders. This article presents a validation of this expert model by measuring the emergence of such knowledge structures in psychotherapy students. SAMPLING AND METHODS: The participants of a continuing education program in cognitive behavioral psychotherapy rated a selection of mental disorders based on their phenomenological similarity. The similarity judgments of each student were translated by nonmetric multidimensional scaling (NMDS) into a cognitive map. In a quasi-longitudinal section design, the maps of the students of the first to the fourth year of training were compared with each other and with an expert map (the expert model) of experienced therapists. RESULTS: The discrepancies of the trainee maps compared with each other and with the expert map significantly decreased with increasing training level. CONCLUSIONS: The convergence of the students' maps towards the expert model indicates that the structural knowledge about mental disorders of experienced therapists can also be found to be emerging in psychotherapy students. This finding supports the validity of the expert model and may reflect a general knowledge-structuring principle of the mental disorders. In spite of the statistical significance found, in view of the small number of participants in the third and fourth years of training, the results should be treated with caution and should be regarded as first indicators which need further confirmation.