The aim of this paper is to closely explain the purpose of treatment of prisoners in penal institutions. Therapeutic communities, resocialisation and rehabilitation are processes which contribute to learning acceptable patterns of behavior, the reduction of aggressive impulses, to the accommodation to life in penal institutions and to the preparation of prisoners for release. It is important to know that there is a problem in balancing between treatment and punishment, where treatment is understood as something positive, and punishment as negative, and the primary function of penal institutions is to punish and make prisoners feel uneasy. The right balance between these two terms leads to positive outcomes of prison's processes and to the reducement of recidivism, also the return in penal institutions. Treatments which are conducted in penal institutions must be modified because of the reduced possibilities of movement, the separation of males and females and the rigidity of laws and lack of available resources. In the end, prison staff has a very important role in all treatments because they are in charge of conducting the treatments and focusing the prisoners towards positive changes.