Objective
Without specific etiology or effective treatment, chronic fatigue syndrome (CFS) remains a contentious diagnosis. Individuals with CFS complain of fatigue and poor sleep symptoms that are often attributed to psychological disturbance.

Methods
To assess the nature and prevalence of sleep disturbance in CFS and to investigate the widely presumed presence of psychological maladjustment we examined sleep quality, sleep disorders, physical health, daytime sleepiness, fatigue, and psychological adjustment in three samples:

• individuals with CFS
• a healthy control group
• individuals with a definite medical diagnosis: narcolepsy

Results
Outcome measures included physiological evaluation (polysomnography), medical diagnosis, structured interview, and self-report measures. Results indicate that the CFS sample had a very high incidence (58%) of previously undiagnosed primary sleep disorder such as sleep apnea/hypopnea syndrome and restless legs/periodic limb movement disorder. They also had very high rates of self-reported insomnia and nonrestorative sleep.

Conclusion
Narcolepsy and CFS participants were very similar on psychological adjustment: both these groups had more psychological maladjustment than did control group participants. Our data suggest that primary sleep disorders in individuals with CFS are underdiagnosed in primary care settings and that the psychological disturbances seen in CFS may well be the result of living with a chronic illness that is poorly recognized or understood.