In some forms of sexual perversion, sexual satisfaction is achieved only by treating one's partner violently (sadism) or conversely, by suffering pain (masochism).

The objectives of our study were to understand the complex relationship between psychotic and perverse structures, and discuss the importance of some criminal risk factors for psychotics who have sexually perverse behaviors, through clinical observation and review literature.

Mr AB was 35-year-old, single and unemployed. He was hospitalized in our forensic psychiatric department following a dismissal for criminal responsibility for an act of emasculation on a child aged 5 years without sexual abuse. In his biography we have objectified cruelty to animals, charged judicial history (imprisonment for theft, murder and escape from prison, hetero aggressive acts) and substance use.

The patient explained with indifference that he heard voices making fun of his “sexual impotence and loss of his manhood”. The day of the forensic act, he got an uncontrollable urge to emasculate the first man he met on his way at the behest of this hearing hallucinatory activity. Psychiatric experts retained the diagnosis of psychosis with perverse arrangements. Under neuroleptic treatment, psychotic symptoms disappeared but the patient's sadistic problems remained present and active throughout his hospitalization.

The following case illustrates the issue of dangerousness and responsibility in a perverse psychotic author assault of a sexual nature. Given their clinical history, the path between perversion and psychosis shows that perverse manifestations are prior to the first psychotic symptoms and the perverse constitution is developed parallel to the psychotic illness.

The authors have not supplied their declaration of competing interest.