Suicidal patients often report problems with their sleep. Although sleep-related complaints and EEG (electroencephalographic) changes have been seen widely across the spectrum of psychiatric disorders, sleep complaints such as insomnia, hypersomnia, nightmares, and sleep panic attacks are more common in suicidal patients. The subjective quality of sleep as measured by self-rated questionnaires also appears to be more disturbed in suicidal depressive patients. Sleep studies have reported various polysomnographic findings including increased REM (rapid eye movement) time and REM activity in suicidal patients with depression, schizoaffective disorder, and schizophrenia. One mechanism responsible for this possible association between suicide and sleep could be the role of serotonin (5HT). Serotonergic function has been found to be low in patients who attempted and/or completed suicide, particularly those who used violent methods. Aggression dyscontrol appears to be an intervening factor between serotonin and suicide. Additionally, agents that enhance serotonergic transmission decrease suicidal behavior. Serotonin has also been documented to play an important role in onset and maintenance of slow wave sleep and in REM sleep. CSF 5-HIAA levels have been correlated with slow wave sleep in patients with depression as well as schizophrenia. Moreover, 5HT2 receptor antagonists have improved slow wave sleep. Further studies are needed to investigate the possible role of sleep disturbance in suicidal behavior.