Aims: To explore the locus of health control in adolescents with chronic fatigue syndrome (CFS) and their parents in comparison with healthy adolescents and their parents. Methods: In this cross-sectional study 32 adolescents with CFS were compared with 167 healthy controls and their respective parents. The Multidimensional Health Locus of Control (MHLC) questionnaire was applied to all participants. Results: There was significantly less internal health control in adolescents with CFS than in healthy controls. An increase of internal health control of one standard deviation was associated with a 61% reduced risk for CFS (OR = 0.39, 95% CI 0.25 to 0.61). Internal health control of the parents was also protective (OR fathers: 0.57 (95% CI 0.38 to 0.87); OR mothers: 0.74 (95% CI 0.50 to 1.09)). The external loci of health control were higher in adolescents with CFS and in their parents. Increased levels of fatigue (56%) were found in the mothers of the adolescents with CFS, in contrast with the fathers who reported a normal percentage of 13. Conclusions: In comparison with healthy adolescents, adolescents with CFS and their parents show less internal health control. They attribute their health more to external factors, such as chance and physicians. This outcome is of relevance for treatment strategies such as cognitive behaviour therapy, for which health behaviour is the main focus. C hronic fatigue syndrome (CFS) is mainly characterised by a complaint of chronic and disabling fatigue in addition to other symptoms. A great variety of explanations have been explored, including infectious, metabolic, immunological, and endocrine causes, but no one factor can be shown to be the single causative agent. Similarly, a single psychiatric cause cannot be established, although comorbidity with depression and anxiety is common in CFS adolescents.1 There is currently insufficient support for either a purely somatic or psychic chain of causation. CFS is believed to have a multifactorial origin, and a distinction is made between constitutional, initiating, and perpetuating factors on both a biological and psychosocial level. and seem to depend much on criteria and methods. Selfreported CFS yields a higher prevalence rate than physician reported CFS, which is the basis for the prevalence rate in the Netherlands. 3 A more recent prevalence study in the UK based on physicians' reports of severe unexplained fatigue of at least three months' duration, reported a prevalence rate of 0.06%. 6 A recent study showed that two thirds of children with CFS finally recover with a resumption of social activities and school attendance and a marked decrease in number and severity of symptoms.7 Although most adolescents recover, disability during illness is high and affects all aspects of life. [8][9][10][11][12] This disability may have lasting effects and it is therefore important to detect factors that influence the start and the course of the CFS symptomatology.The lack of a definite aetiology for CFS limits the treatment options to symptomat...