Theformof criminal actions by young adult men was analyzed for evidence of symptoms indicative of dysfunctioning of the frontal lobe system (FLS), which myelinates late. The inability to switch the principle of action (POA) appropriately during an ongoing activity, when intervening circumstances call for such a switch, is one of the most characteristic signs of FLS dysfunction. The other major sign, the inability to plan, is apparently outgrown during childhood. Some criminal persons seem to show such an inability to switch POA, according to our clinical observation. It is hypothesized that there exists a subgroup of criminals who are unable to switch POA within a heirarchy of principles, and that they will be revealed by the already established Trail Making Test B (TMT-B), and by the new brief clinical Narratives Test (NT).The test results on 30 criminals corroborate the hypothesis. On the Narratives Test, 36 per cent, and on the Trail Making Test-B, 33 per cent of young adult men charged with criminal acts (serving sentences of up to 2 years) demonstrated specifically immature action behavior indicative of FLS dysfunctioning. There is a significant positive association (π= .68,p<.001) between the performance on the two tests.Probable etiological factors include a developmental lag in the myelinization of the frontal lobes, such as is associated with deprivation of practice in their functions; however, pathology, particularly due to trauma, has yet to be ruled out.