Abstract: The author gives special attention to the specificity of a circumstance in proof in criminal cases against minors who committed a socially-dangerous act being mentally disturbed or minors who suffered from mental disturbance after the crime. The author attempts at proving the conclusion about the independency of a circumstance in proof in this category of criminal cases. Besides, the author presents the set of circumstances subject to proving in the proceedings on compulsory measures of medical character. The article describes the term “other circumstances significant for a criminal case” and considers the significance of a special circumstance in proof in proceedings on compulsory measures of medical character. The author uses the dialectical method of cognition and the principles of unity of analysis and synthesis and comprehensiveness. The author formulates the set of circumstances subject to proving in the proceedings on criminal cases against minors suffering from mental disturbances, and states that these circumstances form a special independent circumstance in proof containing circumstances listed in articles 73, 421 and 434 of the Criminal Procedure Code of Russia.