M ultiple sclerosis (MS) is the commonest cause of neurological disability in young and middleaged adults. 1 The characteristic pathological features are demyelinating plaques, astrocytic gliosis and immune-mediated inflammation anywhere within the CNS, with the periventricular region, brainstem, juxta cortical region, optic nerves and spinal cord being particularly common targets. The neurological manifestations are diverse, although they usually reflect the function of the affected anatomical site, and the course of the illness is variable and initially difficult to predict with accuracy.In 80-90 per cent of cases, MS is relapsing-remitting in nature with two-thirds of these cases developing a secondary progressive form of the condition a variable number of years after onset and a third having a relapsing-remitting course that does not result in long-term serious disability. The remaining 10-20 per cent of patients have a primary progressive course with gradually worsening symptoms. 2 The prognosis can be poor in the long term but progression is frequently slow; recent evidence suggests a median of 28 years before a stick is required for walking. 3 The UK annual incidence of MS is 10 in 100 000 with a prevalence of 200 in 100 000. 4 There is estimated to be over 100 000 people suffering from the condition in the UK. The median age of onset is 31 years and it is approximately twice as common in women. 5 It has a multifactorial aetiology with genetic and environmental factors shown to be important. There is 31 per cent monozygotic concordance compared to 5 per cent in dizygotic twins 6 while the environmental influence is demonstrated by marked variations in prevalence in genetically homogenous populations. 7 Prevalence increases with increasing distance from the equator and those who emigrate in childhood have prevalence rates consistent with their adopted country. 8 MS commonly presents with weakness, tingling or numbness in the limbs; diplopia, visual loss or impaired visual acuity; vertigo; dysarthria and ataxia; fatigue; and bladder and bowel disturbance. 5 The array of presenting symptoms in MS can lead to diagnostic uncertainty and neuropsychiatric conditions such as somatisation disorder are sometimes suspected. A study demonstrated that 16 per cent of patients with MS had been referred to a psychiatrist between the onset of neurological symptoms and diagnosis of MS. In spite of neurological symptoms being present in the majority of cases, these remained largely overlooked and diagnoses of conversion disorder and hysterical personality disorder were applied, 9 although the increased use of MRI scans since this finding was reported has improved diagnostic accuracy. While neurological features are the most recognised manifestations of MS, psychopathology, including affective, psychotic and cognitive disorders, is also common. The identification of these symptoms is often more difficult and diagnosis can be delayed. Psychiatric symptoms can occur at onset or later in the MS disease process and initial psych...