This question is complex and does not have a definitive answer. The CDC four-city surveillance study of CFS identified a population of patients that was 98% Caucasian and 85% female, with an average age at onset of 30 years. More than 80% had advanced education and one-third were from upper income families. However, these data included only patients who were under a physician's care. There is now evidence that CFS affects all racial and ethnic groups and both sexes. The Seattle study found that 59% of the CFS patients were women. Eighty-three percent were Caucasian, an underrepresentation, since over 90% of the patients in the study were white. CDC's San Francisco study found that CFS-like disease was most prevalent among women, among persons with household annual incomes of under $40,000, and among blacks, and was least common among Asians and whites. Adolescents can have CFS, but few studies of adolescents have been published. A recently published CDC study documented that adolescents 12 to 18 years of age had CFS significantly less frequently than adults and did not identify CFS in children under 12 years of age. CFS-like illness has been reported in children under 12 by some investigators, although the symptom pattern varies somewhat from that seen in adults and adolescents. The illness in adolescents has many of the same characteristics as it has in adults. However, it is particularly important that the unique problems of chronically ill adolescents (e.g., family social and health interactions, education, social interactions with peers) be considered as a part of their care. Appropriate dissemination of CFS information to patients, their families, and school authorities is also important.