By assigning management of health care in prisons (previously the responsibility of prison administrations) to the hospital sector, the reform of 18 January 1994 brought a public health policy framework into penitentiaries. Beyond provision of primary care, the law called on hospital staff to promote prevention. Although focused on the release and reinsertion of the prisoner into society, programming for health education also targeted a marginal improvement in daily life while in prison. This emphasis on prevention in many ways involved a “medicalising” of the penal institutions. An assessment of this phenomenon based on questioning professionals about their own practices allows the author to identify the contradictions that they face daily, without de-legitimating their actions.