The author analyses new principles for co-operation between psychiatrists and psychologists in writing expert reports resulting from the new Penal Code and Code of Penal Procedure of June 6, 1997. New solutions were introduced in the new legal regulations, which should be seen as an improvement on those in the previous regulations. These concerned, among other things, the role of expert psychologists in deciding what safety measures to adopt, and the possibility of issuing comprehensive joint psychiatric and psychological expert opinions (reports) in cases concerning the soundness of mind (responsibility) of the perpetrator. The co-operation between psychiatrists and psychologists in writing expert reports as envisaged by the new legislative model, however, does not entirely reflect the real competencies of psychiatrists and psychologists; furthermore, the model reveals a lack of internal cohesion and consistency.