Conversion disorder (now also called functional neurological symptom disorder) describes symptoms (of motor and sensory dysfunction such as limb weakness, tremor, visual loss, with or without ‘blackouts’), which can be positively identified as being inconsistent with neurological disease. The disorder is common in neurological services and frequently seen by psychiatrists working in such settings. It is often associated with chronic severe disability. The diagnosis previously hinged on the neurologist’s demonstration of the lack of disease and the psychiatrist’s hypothesis of a ‘conversion’ of stress into a physical symptom. It is now based on positive findings on neurological assessment supplemented by a psychiatric assessment to confirm the diagnosis. Comorbid anxiety and depression disorders are common. Treatment is multi-disciplinary. Explanation of the condition to the patient is a crucial initial step supplemented, where necessary, by psychological treatment (especially for dissociative or non-epileptic attacks) and physiotherapy for functional motor symptoms. The prognosis without treatment is poor once the disability is established.