Society has cherished its fear of psychiatrically ill over the ages. This fear is even more present if concerning mentally ill persons which have already shown socially unacceptable behaviour, or committed serious criminal act before, i.e. murder or rape. This kind of criminal acts, regardless of it's every - day presence in all social groups, gets all the media attention. It is a fact that there are no valid data regarding the rate of criminal activity among psychiatric patients and the percentage of that activity compared with «normal» population, nor can we find the information about the rate of recidivism in these two social groups. But, it is also a fact that criminality of mentally ill stays stabile trough the years, as well as that some diagnostic categories are more vulnerable for demonstrating violent behavior.

The purpose of this study was to compare aggressiveness between two groups of patients: patients conducting security measures and control group - patients hospitalized because of exacerbation of psychosis. The study included 40 patients on security measures and 40 patients from control group, diagnosed according to ICD 10 diagnostic criteria. Risk of violence was assessed using instruments of clinical assessment: OAS, PCL:SV and HCR - 20 Scale, at the admission of patients. The results of statistical analysis are that there is no statistically significant difference between two groups regarding the violent behavior and risk for violence in the future. Two diagnostic categories are prominent in showing aggressive behavior: paranoid psychosis and paranoid schizophrenia.