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Chronic fatigue syndrome is defined as a severe disabling fatigue which lasts for several months. The fatigue is made worse by minimal physical or mental exertion, and there is no adequate medical explanation for the fatigue.

NICE state that (1):

  • a diagnosis should be made after other possible diagnoses have been excluded and the symptoms have persisted for:
    • 4 months in an adult
    • 3 months in a child or young person; the diagnosis should be made or confirmed by a paediatrician
  • the diagnosis of CFS/ME should be reconsidered if none of the following key features are present:
    • post-exertional fatigue or malaise
    • cognitive difficulties
    • sleep disturbance
    • chronic pain
  • severity of CFS/ME is defined by the degree to which CFS/ME affects a person's functioning and daily life (1):
    • mild CFS/ME
      • people are mobile, can care for themselves and can do light domestic tasks with difficulty. Most are still working or in education, but to do this they have probably stopped all leisure and social pursuits. They often take days off, or use the weekend to cope with the rest of the week
    • moderate CFS/ME
      • reduced mobility and are restricted in all activities of daily living, although they may have peaks and troughs in their level of symptoms and ability to do activities. They have usually stopped work, school or college and need rest periods, often sleeping in the afternoon for 1 or 2 hours. Their sleep at night is generally poor quality and disturbed
    • severe CFS/ME
      • unable to do any activity for themselves, or can carry out minimal daily tasks only (such as face washing, cleaning teeth). They have severe cognitive difficulties and depend on a wheelchair for mobility. They are often unable to leave the house, or have a severe and prolonged after-effect if they do so. They may also spend most of their time in bed, and are often extremely sensitive to light and noise

The Oxford criteria for the diagnosis of chronic fatigue syndrome are outlined in the menu item.


  1. NICE (August 2007).Chronic fatigue syndrome/ myalgic encephalomyelitis (or encephalopathy) Chronic fatigue syndrome/myalgic encephalomyelitis (or encephalopathy): diagnosis and management of CFS/ME in adults and children

Last reviewed 01/2018