SUMMARY In recent years, mass violence associated with men who identify as involuntary celibates (incels) has been of increasing concern. Incels engage in an online community where misogyny and incitements to violence against women are prevalent, often owing to the belief that women are denying them a ‘right’ to sex. Indeed, inceldom can be considered a form of extremism. Information released about the prepetrators of incel-associated violence consistently suggests that mental disorder is a contributory factor and may increase vulnerability to engaging with the incel community. Depression, autism and personality disorder are particularly relevant. To date, there has been little research into the mental health of incels and how, in some, this contributes to violence. This article considers the associations between mental disorder and inceldom, including the risk factors for incel-related violence, and makes recommendations for best practice in risk assessment and clinical intervention.