Munich ME/CFS Cohort Study

Inclusion Criteria: * Written consent of the patient (or legal guardian for patients aged \< 18 years). * Age 0 - 25 (including) * Documented or probable acute infectious disease at the onset of ME/CFS symptoms * Diagnosis of ME/CFS according to the IOM criteria, the CCC, the diagnostic worksheet published by P.C. Rowe et al. (2017), or the pediatric case definition published by L.A. Jason et al. (2006). Exclusion Criteria: • drug/medication abuse, major surgery within the last six months, presence of organ failure, post-stroke/craniocerebral trauma with cognitive deficits, post-intensive care syndrome, syphilis, Lyme disease, AIDS, hepatitis B/C, multiple sclerosis, systemic lupus erythematosus, Sjörgren's syndrome, malignancy, major depression or other severe psychiatric illness, primary sleep disorder, severe endocrine disease (e.g., hypopituitarism, adrenal insufficiency), and other conditions that might explain ME/CFS symptoms.