Successful psychological and physical adaptation in late life correlates with preservation of sleep quality and physiological integrity of nocturnal EEG sleep measures. Failure to adapt is associated with loss of sleep continuity, alterations in the temporal distribution of delta wave activity, and by either a relative increase in REM sleep (e.g. in mood disorders) or a decrease in REM sleep (e.g. neurodegenerative disorders). Maintenance of sleep (particularly REM sleep) into late life may not be just a correlate, but also possibly a mechanism, of successful aging and thus necessary to the long-term maintenance of vitality and engagement in life.