Résumé : Objective: The chronic fatigue syndrome (CFS) is a debated clinical entity, not presently associated with specific sleep abnormalities. However, higher levels of deep sleep and/or lower levels of light sleep have been reported in several all-night polysomnography studies in CFS patients. This distribution of Non-Rapid Eye Movement Sleep (NREMS) contrasts with what would be expected if sleep was interrupted by microawakenings, such as in sleep apneas or periodic limb movements, where more light sleep and less deep sleep are commonly observed. This "paradoxical" distribution of NREMS could represent a characteristic feature of chronic fatigue and deserved to be investigated. Methods: A retrospective comparison of the NREMS distribution was performed between 28 "pure" Chronic Fatigue Syndrome patients (without primary sleep or psychiatric disorders), 27 Apneic-Hypopneic patients and 27 Healthy Controls. Results: Data showed CFS patients to have a higher stage 4/stage 2 or stage 4/light sleep ratios than the other two conditions. Conclusion: This sleep pattern is closer to what is observed in cases of infections than to what is seen after sleep fragmentation by primary sleep or in psychiatric disorders. Such a particular sleep pattern could provide insights into the pathophysiology of fatigue. Copyright © by The Haworth Press, Inc. All rights reserved.