People with chronic fatigue syndrome (CFS) are generally 25 to 45 years of age. Women are more likely to have CFS.

CFS is rare in children. It may occur in teenagers, especially young teenage girls. Unlike adults, teenagers are more likely to develop CFS after having an illness such as mononucleosis or flu.

Various studies report that between 1 and 5 people per 1,000 in the United States may have CFS-enough to call it a major public health problem.⁴