The vulnerability of patients of late age in psychiatry increases the professional and ethical requirements to the quality of psychiatric and forensic psychiatric help. It must account for the clinical and dynamic features of mental disorders in old age, biopsychosocial determinants of their formation, be based on a conceptual approach and a comprehensive understanding of the involution processes. To identify biopsychosocial determinants of mental disorders in old age and (or) involving patients to the forensic psychiatric examination, we examined 235 late age patients in criminal and civil cases. Revealed: «non-dement» mental disorders – with 45.5%, psychosis – with 7.7%, dementia – with 46,8%. The results of biopsychosocial determinants of involution are determined as follows: biological: sensory and motor deprivation, multicomorbid somatic neurological pathology, specific syndromes and disorders if late age, dementia; socio-psychological: termination of labor activity, living alone and loneliness, problematic relationship with children because of housing disputes and alcohol; legal: conclusion and contestation of legal civil acts, participation in criminal proceedings as victims and defendants, legal illiteracy, legal controversy, lack of legal protection; victimological: physical (assault, abuse), psychological (threats of commitment into social security institutions, involuntary commitment to a psychiatric hospital and examination by a psychiatrist, hold in the psychiatric hospital), financial violence (fraud with housing for older people and deception, manipulation during conclusion of civil-legal acts), violation of rights of older person (unlawful deprivation of legal capacity).