Polish criminal law states that sixteen-year-old offenders who have committed grave offenses and seventeen-year-old minor offenders may, depending on the court verdict, be tried according to the Juvenile Delinquent Act or the Criminal Law Act. Both acts require a different range of psychiatric and psychological assessment as well as different expert skills. In the case of sixteen- and seventeen-year-olds it is necessary to submit both kinds of assessment findings, since only jointly can they adequately inform the court. The present authors observe that these assessments should be conducted by two separate groups of experts and that the forensic-psychiatric expertise should follow the psychological-pedagogical one. The authors also believe that both assessments should tackle the crucial problems stated in art. 9 par. 2 and 3 of the Criminal Law Act, i.e., whether the offender is psychologically and socially mature enough to be liable to penalty or whether only educational and corrective measures should be applied.