A diagnosis is based on persistent symptoms as below: Compulsory symptoms: Impaired function Post-exertional symptoms Fatigue In addition, 2 of 3 groups of symptoms are required: Sleep problems Cognitive problems Pain A diagnosis is made if all the criteria below apply: Symptoms are persistent for 6 months (or for 3 months if post-infection) and at least some occur daily and are at least of moderate severity Other diagnoses are excluded by history, physical examination, and medical testing, including learning disabilities Severity of symptoms over a pre-determined cut-off score