Sexuality and prison are two mutually exclusive words, opposing pleasure and corporal punishment. The aims of this data collection on sexual practices in prison were to assess how strong preconceived ideas on sexuality remained among inmates, and the shame and guilt surrounding those practices, but also to grasp the defence mechanisms used by prison professionals, including nursing staff. This work, although it suffers from many biases, represents a first inventory of sexual practices to be compiled within Lille prison and is the first attempt at finding the best investigation method to assess such a difficult topic. This research has also helped to confirm the existence of homophobia and major taboos about sexual practices in jail, on the part of both males and females, with a great ignorance of sexuality in general and difficulties in overcoming preconceived ideas on this issue. The main concern of the inmates interviewed was to try to comply with the expected norms, showing the weight of Judaeo-Christian values. In addition, there are many forms of reticence and defence mechanisms at play amongst professionals, including nursing staff, raising the question of how interventions on sexuality in a prison environment might be helpful, not only for inmates, but also for staff, by means of an institutional prison project.