We present a case of violent sleep-related behaviour in a patient with narcolepsy with cataplexy (NC) and REM sleep behaviour disorder (RBD), causing injuries to his wife that resulted in charge of assault, followed by a divorce case. This observation pinpoints that RBD in NC can arise early in a patient's life and that it can be violent, that pharmacological treatment for RBD has to be considered in this case, that lack (or delay) of RBD diagnoses may further exacerbate the psychosocial burden of NC, and that a general awareness of the nature of sleep related violence may avoid unfortunate legal and personal consequences for patients, their partners and families.