Purpose: The purpose of this article is to make an attempt to apply diagnostic model for qualification contents as delusional on the basis of a clinical case. Method: The applied method is the analysis of the patient with a history of ischemic stroke, developing delusional beliefs. Results: The authors indicated a pretty good applicability of diagnostic model in the commented case, at the same time, formulating guidance on the need to expand and change some of the criteria with the possibility to complement the model with elements from neurobiological models. Conclusions: The case analysis allowed the authors to point out strengths and weaknesses of the discussed diagnostic model. The authors postulate that strictly neurobiological categories should be replaced by those that allow the occurrence of cognitive deficits, as well as they formulate a statement that the problems with inference, as one of the basic factors forming delusions, should not be analyzed only in terms of the damage to the right hemisphere.