Abstract: Based on the review of the latest empirical researches, the authors of the present article examine and specify the role and importance of the parents' treatment of teenagers in the development of teenager's basic mental formations and solution of the most important psychological goals of their age. When describing substantial features of the aforesaid stage of human ontogenesis, special attention is paid to the subjective feeling of loneliness experienced by a teenager. The emphasis is made on contradictory interpretations of this phenomenon in modern academic literature. The authors provide a theoretical basis of their empirical research. The research involves 56 school students (teenagers). The authors analyze the relationship between their subjective experience of loneliness, their mother's and father's treatment and the quality of their social-psychological adjustment. The authors have used such methods of psychological diagnostics as: The Subjective Loneliness Scale by S. V. Dukhnovsky, Teenagers about Parents of E. Shafer as adapted by L. I. Vasserman, I. A. Gorkovsky and E. E. Romitsyn, and The Test of Social-Psychological Adjustment by C. Rogers-R. Diamond adapted by T.V. Snegireva. The main conclusions of the research: the subjective feeling of loneliness experienced by a teenager within the average values is normal and caused by teenager's reflection processes and age; the mother's treatment of a teenager conditions the relationship between a teenager's subjective experience of loneliness and the quality of his or her social-psychological adjustment; the subjective feeling of loneliness experienced by a teenager correlates to his or her mother's Hostility and Inconsistency; and the quality of social-psychological adjustment of a teenager correlates to his or her mother's Directivity and Positive Interest. The research results allow to define goals for further research in order to find out whether it is possible to use the subjective feeling of loneliness experienced by a teenager as an indicator of his or her psychological problems and risks of deviant behavior providing that qualitative and quantitative characteristics of his or her feeling of loneliness have been clarified in terms of their relationship with the social situation where a teenager grows.