OBJECTIVES:: Alzheimer disease (AD) has been associated with diminished function of the biological clock in the suprachiasmatic nuclei (SCN) and pronounced circadian sleep-wake cycle disturbances. Few studies have investigated other dementia etiologies. Because alcohol acts on the SCN and modifies circadian rhythms in animal studies, Korsakoff psychosis (KP) may also be associated with circadian rhythm abnormalities. This pilot study investigated the rest-activity cycle of KP to see whether there were sleep-wake cycle disturbances similar to those that the authors had observed in patients with AD. DESIGN AND SETTING:: Cross-sectional observational study in a single academic medical center. PARTICIPANTS, MEASUREMENTS:: The authors investigated the circadian rest-activity cycle of six moderately demented patients with KP who wore an activity/lux monitor for 10-26 days and compared these patterns with those of six home-living healthy individuals of the same age group. In addition, rest-activity cycle data from previous studies of patients with AD were examined. INTERVENTIONS:: None. RESULTS:: The rest-activity cycle of KP was remarkably well entrained, without the marked circadian and sleep disturbances found in patients with AD on the same ward. KP had a >2 hour earlier bedtime and rest onset than healthy subjects and a 30-minute earlier wake-up time, resulting in longer nocturnal rest duration. The major difference was a greatly diminished daytime activity level and extremely low light exposure. CONCLUSION:: A stably entrained, although low-amplitude and phase-advanced rest-activity cycle may reflect the different neuropathology of demented patients with KP compared with patients with AD.