In this article an outline is given of the implications for a sociotherapeutic approach, theoretically based on principles of a learning theory, in an institutional setting treating mentally ill deliquents. The sociotherapist is described as a cotherapist in a multidisciplinary treatment program. His role is connected to a systematically planned complex of relevant target behaviours of the inmates, starting within the institution and ending in behavioral training situations in society. Learning theory has specific implicatons for the sociotherapist's approach, for his education and for his identity.