Researchers screened a random sample of 10,119 youth ages 5-17 from 5,622 households. Of those who screened positive over the phone, 165 youth went on to medical and psychiatric examinations. Following evaluations, a team of physicians made final diagnoses. Youth were given a diagnosis of ME/CFS if they met criteria for case definitions. Of the 42 youth diagnosed with ME/CFS, only 2 (4.8%) had been previously diagnosed with the illness.