Mothers in prison are at high risk of depression and other mental health issues and yet access to therapeutic services is limited. This paper describes the development by the author of two prison therapy groups: one for pregnant women, the other for mothers and their babies. Called the ‘Born Inside’ project, both groups are currently held in Bronzefield Prison, Surrey. The theory and principles behind the project are discussed, as well as the processes and practicalities involved in providing the therapy and specialised support to the women and their vulnerable infants. In addition, principles of forensic psychotherapy in relation to this specific prison population are described, and the situational and emotional challenges faced are illustrated through narratives of group members.