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Objective To study sleep–wake and body core temperature (BCT) circadian rhythms in patients with multiple sclerosis (MS)-associated with chronic fatigue. Methods Six relapsing–remitting MS patients with chronic fatigue underwent 48 consecutive hours polysomnography (PSG) with BCT measurement, followed by a Multiple Sleep Latency Test (MSLT). All patients were relapse- and drug-free. Mood depression, brain and cervical cord enhanced MRI, dynamic spirometry and Fatigue Severity Scale (FSS) were assessed just before PSG. Results In all patients mood depression was absent and dynamic spirometry normal, but FSS confirmed fatigue. MRI showed non-enhancing lesions. Nocturnal sleep was characterized by normal architecture and mean sleep efficiency was only slightly reduced. Arousal index was normal and periodic limb movements during sleep (PLMS) were present in four patients, with an increased index (PLMS- I ) in only two of them. Upon MSLT, mean sleep latency was normal in all patients with one sleep onset REM period in one patient. All patients displayed a normal BCT 24-h rhythm. Mesor, amplitude and acrophase of BCT rhythm did not show significant differences between MS and controls. Conclusions We found substantially normal sleep–wake and BCT rhythmicity in six patients with MS and fatigue. Non-restorative sleep and abnormal BCT regulation were unlikely mechanisms of chronic fatigue in our MS patients. Significance Subjective fatigue and abnormal sleep and BCT can be independent manifestation in MS patients. The findings support the notion that objective measures of fatigue comparable to the MSLT for sleepiness do not exist.