Over the past decades, the Trans-Baikal Territory has been characterized by a steady upward trend in juvenile delinquency rates; among children and adolescents, a high incidence rate of mental and behavioral disorders is recorded. Aim of the study: to study the factorial causation of mental disorders and illegal behavior in adolescents of the Trans-Baikal Territory. The work is based on the analysis of 1035 reports of outpatient forensic psychiatric examinations of adolescents-offenders (aged 15 to 17 years) included in the main group, from which two subgroups are distinguished: adolescents with an established psychiatric diagnosis (945) and healthy adolescents (90). The control group consists of 269 adolescents who have not been brought to the police and have not committed criminal acts. It is established that the mental health of adolescents with offensive behavior in the Trans-Baikal Territory depends on a set of interacting factors (hereditary, biological, socioeconomic), of which the highest degree of influence is possessed by alcoholism of parents, upbringing in an orphanage, low financial level of the family, pathology of pregnancy and childbirth. The presented unfavorable factors also contribute to the formation of criminal behavior in the adolescents' contingent.