AbstractBackground: Globally, the frequency of discrepancies between clinical and forensic medical diagnoses is about 30%. The most common errors made during determination are the main disease pathogenesis and tanatogenesis. Aims: To identify the causes of incorrect diagnosis determination and suggest the rules for the precise diagnosis formulation. Materials and methods: A retrospective analysis of the forensic medical deontological examinations from the case history data of the State Forensic Medicine Service has been done from 1984 to 2014. There were 1192 forensic medical deontological examinations. A descriptive method was used. The foreign literature data were analyzed in order to compare the results for a comprehensive study. Results: 1192 deontological expertise were analyzed during 1984–2014. This study revealed that 37% of clinical and forensic medical diagnoses did not match completely, 24% – matched partially, and 37% – matched. Majority of the discrepancies between diagnoses were identified of surgeons – 13.42%, obstetricians-gynecologists – 8.10%, neurosurgeons – 7.34%, 23% of all cases when a person was treated at the intensive care unit. Conclusions: More common discrepancies between diagnoses were identified of surgeons, obstetricians-gynecologists, neurosurgeons and when a person was treated at the intensive care unit. Frequency of discrepancies between clinical and forensic medical diagnoses is growing. The correct formulation of the clinical diagnosis is the first step toward a proper treatment. The final diagnosis should consist of three sections: main disease/injury, pathology followed by the complications and the accompanying conditions of the patient.