Sleep disorders and depressive symptoms are concomitant features in patients with addictive disorders. In this study, patients with addiction (alcohol and opioid, resp.) and with major depression (DSM-III-R) were examined with a sleep EEG and compared to age-matched controls. An age-dependent decrease of total sleep time and slow-wave sleep (SWS) was demonstrated. Sober patients with alcohol dependency showed a decrease of SWS, whereas patients with opioid dependency substituted with methadone showed a disorder of REM sleep (REM suppression). Depressive patients revealed a disturbance of sleep continuity and REM sleep (increased REM sleep). The neurobiological differentiation by sleep EEG is of interest for research and clinical practice.