The practice of psychiatry and psychology in prisons is essential because of the high prevalence of mental disorders that is observed. Psychiatrists and psychologists, such as other health care professionals, should be affiliated to the health department and intervene in the therapeutic role, which must be distinguished from the role of the psychiatric expert mandated by the court. Therapy in prison is challenging because of the sometimes contradictory issues, at the interface of clinical, societal, security, legal and political fields. Health care professionals can thus be subject to important pressures or to ethical and deontological issues.