The author presents a systematic analysis of the causes of errors in forensic-psychiatric opinions. He bases his analysis on his thirty-year-long practice and a review of the literature. He distinguishes three different types of errors: (l) unwitting errors resulting from the methodological shortcomings of forensic psychiatry, lack of homogeneous principles for the preparation of opinions, incorrect diagnosis, ignorance of the law, discrepancies between the languages and conceptual apparatuses of law and psychiatry, incomplete evidence and medical documentation, inadequate evaluation of the motive of the offence and the offender's modus operandi, lack of forensic-psychiatric competence; (2) deliberate errors resulting from emotion, the expert's attitude of renowning, acceptance of subjective attorney's and paternalistic attitudes, action taken by the opinionee and his family, the expert's corruption. He presents the principles and methods of action which ought to help the jurisdiction to control forensic-psychiatric opinions. He also points out the need to introduce compulsory training of experts, their attestation, and, in the long-run, specialisation in forensic psychiatry and development of a list of rules of operation and attestation of forensic-psychiatric wards.