Objectives:
The article aims to discuss the psychotherapy of psychosexually immature child molesters. Authors present diagnostic criteria of psychosexual immaturity, which in psychological-sexological practice is most commonly recognized within unspecified ICD-10 F66.8 category that represents other psychosexual development disorders.

Methods:
Diagnostic indicators were selected by defining the concept of sexual maturity and by establishing a contrario characteristics of the state in which they are not fulfilled. For this purpose, biological, psychological and social ways of perceiving psychosexual maturity were described and referred to Bancroft’s [1] eclectic interactional model of sexual development.

Results:
Diagnostic criteria of psychosexual immaturity were defined basing on Bancroft’s [1] three developmental strands: lack of shaped sexual identity, inability to formulate an adequate sexual response and inability to establish a dyadic relationship. Deficits in these areas characterize some child molesters.

Conclusions:
Psychological work with sex offenders should be preceded by the thorough functional diagnosis, which names existing deficits and uses them to build treatment plan. Psychosexual maturity could be used to create and strengthen new, more adaptive sexual behaviors and as a result may help to prevent relapse. Application of the proposed classification for the diagnosis of psychosexual immaturity requires: 1. adoption of a holistic perspective, which integrates various aspects of sexual development, 2. reference to the individual's age, 3. taking into account an internal and external context in which a sexual behaviour occurs, 4. cooperation of a psychologist-sexologist or a physician-sexologist with doctors of other specialties.