BACKGROUND Individual beliefs and cognitions may affect adjustment to chronic fatigue syndrome (CFS) and illness perceptions, in particular, have been reported to correlate with both disability and psychological adjustment to CFS in self-diagnosed cases. OBJECTIVE The aim of the present study was to examine these relationships in a clinic sample of CFS patients assessed by both a physician and psychiatrist. METHODS A sample of 173 patients referred to a multidisciplinary CFS clinic and fulfilling current operational criteria for CFS [Ann Intern Med 121 (1994) 953; J R Soc Med 84 (1991) 118.] were randomly selected from the clinic database and surveyed with the Hospital Anxiety and Depression scale, Fatigue Questionnaire and Illness Perceptions Questionnaire [J Psychosom Res 37 (1993) 147; Psychol Health 11 (1996) 431; Acta Psychiatr Scand 67 (1983) 361.]. RESULTS A total of 126 patients responded (73% response rate). The illness perception components studied were consequences (of illness), illness identity, causes (of illness), the ability to control/cure the illness and (expected) timeline of the illness. These components accounted for 15%, 28% and 30% of the variance in levels of fatigue, depression and anxiety, respectively. Two of the illness perception components (consequences and illness identity) were stronger predictors of fatigue score than mood scores. CONCLUSIONS These findings confirmed in a clinical sample that illness perceptions are associated with variation in both disability and psychological adjustment in CFS. Illness perceptions may have an important and long-lasting effect on adaptation to CFS, and it is necessary to have a greater understanding of their role in order to tailor effective interventions for the condition.