In forensic psychiatry placebo is used rather rarely. It is because forensic psychiatrists don't have enought qualification in this area and they have to work with the special type of patients, who are difficult to communicate and create a rapport with. the patients of forensic psychiatrists always have a conscious intention to simulate or to develope a mental derangement to avoid crimanal liability. Using of placebo in forensic psychiatry gives an opportunity to differ simulation from true mental disorder in a 90% of cases. in subjectively difficult situation (being in prison, incarceration) different mental disorders usually progress. We examined about 100 patients who showed symptoms of different mental aberrations which made it hard to diagnose actual condition of the patient.Placebo procedure is when a patient is given an inert pill, told that it may improve his or her condition, but not told that it is in fact inert. It may make the patient to believe the treatment will change his or her condition and this belief may produce a subjective perception of a therapeutic effect, causing the patient to feel their condition has improved or an actual improvement in their condition. as the result of using the placebo we overcame such symptoms like:· insomnia· headaches · psychic tension· collapse· tremor· hysterical paroxysmal· mutismAfter using of the placebo these symptoms quickly disappeared and we were able to diagnose actual condition of the patient and bring him to justicó.