An aim of the study was to specify peculiarities of the clinical dynamics of organic psychic infantilism and psychopathological presentations of this disorder in adolescence. A significant prevalence of psychic infantilism caused by organic CNS damage in patients seeking psychiatric help in adolescence and a negative effect of this disorder on social adaptation in this period of life were found. Sixty-seven patients, aged 15-18 years, (ICD-10 diagnosis F06) with signs of psychic infantilism were studied. In these cases, psychic infantilism encompassed all aspects of mental activity and manifested itself as a constant personality trait that caused the infantile type of reaction to the most of life situations. The clinical heterogeneity of organic infantilism determined by the different degree of psychic immaturity in some areas of psychic activity and concomitant encephalopathy symptoms was noted. This allowed to single out 3 groups of patients: with domination of psychic infantilism in volition (28 patients), in emotional sphere (21 patients) and immaturity of cognitive functions (20 patients). The clinical heterogeneity of psychic infantilism likely reflects the character of CNS damage (localization and time of the damage) and specifics of related organic dysontogenesis.