A psychological examination of 88 men and 42 women aged between 26 and 88 (116 of them had mental disorders, and 14 were mentally healthy) has been carried out while they were undergoing the complex forensic psychological and psychiatric examination for purposes of assessment a person's deal-making ability at the time of the transaction and diminished capacity. In respect of 46 persons, forensic experts took the decision that the persons ‘were unable to understand the meaning of their actions, regulate and control them at the time of the transaction’; 48 persons were found to be ‘able to understand the meaning of their actions, regulate and control them at the time of the transaction’; and 26 persons were found to be ‘able to understand the meaning of their actions, regulate and control them only if assisted by others’. In respect of 10 persons, the questions posed to forensic experts failed to be definitively resolved. 57 indicators, reflecting the disturbances of cognitive processes, individual psychological peculiarities, and data on socialization had been diagnosed for each of the examinees. Factor analysis made it possible to identify the pathopsychological symptom complexes that are relatively specific for persons who either have or lack the deal-making ability at the time of the transaction (Article 177 of the Civil Code of the Russian Federation), as well as for persons with diminished capacity due to mental disorder (Para. 2 of Article 30 of the Civil Code of the Russian Federation).