WHAT'S KNOWN ON THIS SUBJECT: Adolescent chronic fatigue syndrome (CFS) is a disabling illness. The majority of adolescents with CFS miss significant amounts of school. Little is known about the epidemiology of CFS in adolescents. WHAT THIS STUDY ADDS:The prevalence of adolescent chronic fatigue syndrome (CFS) diagnosed by general practitioners was approximately 111 per 100 000 (0.11%) per year and the incidence of CFS diagnosed by pediatricians was 12 per 100 000 (0.012%) per year. Adolescent CFS is a well-accepted diagnosis among pediatricians but is probably underrecognized by primary health care providers. abstract OBJECTIVE: To determine nationwide general practitioner (GP)-diagnosed prevalence and pediatrician-diagnosed incidence rates of adolescent chronic fatigue syndrome (CFS), and to assess CFS morbidity. DESIGN AND SETTING:We collected data from a cross-sectional national sample among GPs and prospective registration of new patients with CFS in all pediatric hospital departments in the Netherlands. PATIENTS AND METHODS:Study participants were adolescents aged 10 to 18 years. A representative sample of GPs completed questionnaires on the prevalence of CFS in their adolescent patients. Pediatric hospital departments prospectively reported new cases of CFS in adolescent patients. For every new reported case, a questionnaire was sent to the reporting pediatrician and the reported patient to assess CFS morbidity. Prevalence was estimated through the data from GP questionnaires and incidence was estimated on the basis of cases newly reported by pediatricians from January to December 2008. RESULTS:Prevalence was calculated as 111 per 100 000 adolescents and incidence as 12 per 100 000 adolescents per year. Of newly reported patients with CFS, 91% scored at or above cutoff points for severe fatigue and 93% at or above the cutoff points for physical impairment. Forty-five percent of patients with CFS reported Ͼ50% school absence during the previous 6 months. CONCLUSIONS:Clinically diagnosed incidence and prevalence rates show that adolescent CFS is uncommon compared with chronic fatigue. The primary adverse impact of CFS is extreme disability associated with considerable school absence.