The assessment of individuals with personality disorders has always been a challenge since these disorders entered scientific psychiatry at the end of the 19th century through the theory of degeneration under the term psychopathy. This work presents the assessment of personality disorders as a methodically breakable, verifiable process, making decisions at the diagnostic level as well as at the first and second levels of assessment more comprehensible. The outcome is to be submitted to the judge for a decision regarding the pros and cons of diminished criminal responsibility. Additionally, it offers insights into the treatment of patients with personality disorders in secure facilities and the criminal prognostic assessment.