Fibromyalgia syndrome is a common chronic pain syndrome that is often associated with sleep disturbances characterized by subjective experience of non-restorative sleep. The complaints of sleep disturbances are correlated with polysomnographic features showing clear abnormalities in the continuity of sleep as well as in the sleep architecture. Sleep-recording abnormalities are characterized by a reduced sleep efficiency with increased number of awakenings, a reduced amount of slow wave sleep and an abnormal alpha wave intrusion in non rapid eye movement, termed alpha-delta sleep. These data were confirmed by spectral analysis of sleep showing an increased EEG power density in the higher frequency band and a reduced EEG power density in the lower frequency bands. Moreover, other microstructural aspects of sleep were modified with high frequency of arousals and alpha-K complex reported, both indicators of fragmented sleep. The fibromyalgia symptoms may relate to a non-restorative sleep disorder associated with the alpha-EEG sleep anomalies. However, alpha-EEG sleep anomaly is non-specific for fibrositis, also seen in normal controls during stage 4 sleep deprivation. Moreover, fibromyalgia patients may also experience primary sleep disorder such as sleep apnea or periodic leg movements. The etiology of this common condition is incompletely understood and the existence of a specific entity of fibromyalgia is still a matter of debate. However, several studies have found abnormal brain metabolism of substances such as serotonin implicated in sleep arousal and pain mechanisms and administration of tricyclic antidepressants and selective serotonin reuptake inhibitors may be useful in fibromyalgia. Pain, poor sleep quality and anxiety may contribute to the clinical picture. Several factors such as psychological, environmental, genetic factor, altered serotonin metabolism and altered sleep physiology are involved in the pathogenesis of fibromyalgia.