With its verdict in May 2011 the German Federal Constitutional Court declared the current law for preventive detention unconstitutional and obliged the legislative bodies to undertake a freedom- and treatment-oriented reform. Psychiatrists and psychotherapists are bound to provide therapeutic concepts. Currently there is a lack of information on the intended clientele. In our study we examined 26 persons serving preventive detention, 32 regular prisoners and 29 non-delinquent probands. The groups were matched according to age and intelligence. We gathered sociodemographic data, criminal records and conducted the tests SCID I, SCID II und PCL-R, K-FAF and BIS-11 to obtain diagnoses and characteristics. Based on this information, the HCR-20 and GAF were performed. In comparison to regular prisoners and non-delinquents, the group of those serving preventive detention is characterised by medium to advanced age, antisociality, psychopathy, substance abuse or addiction, aggressivity, a strong criminal record, years of imprisonment, insufficient educational and vocational training and a high risk of recidivism. In our examination of persons serving preventive detention, we demonstrate that this clientele is a group of recidivists difficult to treat. The current laws and a lack of early intervention programs have prevented and delayed their timely and possibly successful treatment. From a psychiatric point of view, there is a strong need for new therapeutic concepts to meet this challenge.