The aim of social work in social services in the treatment of a prisoner is the mitigation of social problems or the elimination of their possible causes, and the preparation of a prisoner for release from prison. Social work, social services and social counselling are the specialised forms of care for an individual, the enhancement of his individual potentials, the optimisation of behaviour in the specific moments of his life. A relationship between a prisoner and a social worker is an important milestone which affects the quality of the counselling activity. However, the relationship develops step by step, and the social worker gradually gains trust and authority. However, in the development of such a relationship, the social worker in the helping profession must have certain principles to be followed. Social work in serving custody and serving an imprisonment sentence is a professional activity focused on clarifying the social problems of the prisoners which influenced their criminal activity, or whose existence is a risk factor for the resocialisation prognosis, so-called information assistance, support and counselling focused on limiting the negative effects of the prison environment and eliminating or minimising the causes of social problems. Social work in helping professions with prisoners belongs to a science area of social work. According to the place of work, we can divide social work with the punished persons into two subgroups: social work in the prison – i.e. penitentiary social work; and social work following the imprisonment sentence – post-penitentiary social work.