Forensic psychiatry, as a branch of psychiatry, is a science that largely contributes to interconnection of medical and other sciences, and in particular legal sciences. In addition to the fact that it defines the clinical picture of people with mental illnesses it provides a link to legal issues. Based on forensic psychiatry legal systems can define rights but also sanctions for people with mental illnesses should they violate the rules of conduct provided for or imposed on each person within a particular system. The aim of this diploma thesis is to provide a rather detailed explanation and give insight into the field of forensic psychiatry, show how it is practiced and how it is linked to legal science. Furthermore, this diploma thesis depicts the cases of mental illnesses that we are likely to encounter in everyday life, tells about which one presents major danger for patients with mental diseases themselves, their environment and the way law treats persons who are neither aware of their unlawful acts nor able to control them. All information and knowledge contained in this thesis is obtained on the basis of scientific, professional and other graduate theses, literature written by forensic psychiatry specialists, neuropsychiatrists, professors of medical sciences and many others. Processing this topic for the diploma paper it creates awareness of the need for constant progress in all areas of sciences and the need for science to intertwine for better and more detailed regulation of the world around us.