The severe dissociative disorders of dissociative identity disorder (DID) and dissociative disorder not otherwise specified (DDNOS) are complex, not uncommon presentations associated with severe symptoms, high rates of comorbidity, high service use compared with other psychiatric disorders, and high suicidality. They exact high personal and socioeconomic burdens and show poor response to standard treatments, with high levels of treatment attrition and ‘revolving-door’ out-patient and in-patient service use; patients are often misdiagnosed or labelled ‘untreatable’. DID and DDNOS diagnoses remain controversial, but they have been repeatedly validated internationally over the past 20 years and the disorders can be accurately identified using screening tools and structured clinical interviews. Neurobiological understanding of the disorders is increasing; findings are consistent with a trauma origin and have commonality with features seen in other trauma-related disorders. Specialist treatment that addresses the dissociative symptoms alongside their trauma origins shows promise in early evidence. Working knowledge of these disorders among non-specialist psychiatrists and psychologists in the UK remains poor, resulting in long delays before diagnosis and treatment.. To read the full article, log in using your MPFT NHS OpenAthens details.