Significant changes in sleep/wake patterns, particularly loss of SWS and increased amount and frequency of nighttime wakefulness, apparently occur even at an early stage of the AD process. These disruptions of nighttime sleep increase in magnitude with increasing severity of dementia. While the REM sleep of early stage AD patients is relatively unaffected by the disease process, later stages of AD are marked by significant losses of REM sleep and perhaps more importantly the breakdown of the sleep/wake circadian rhythm with significant amounts of sleep occurring during the day. This daytime sleep is of poor quality however, consisting almost exclusively of stages 1 and 2 sleep and does not compensate for the nighttime losses of SWS and REM sleep experienced by AD patients. These findings clearly support the clinical observations and anecdotal reports of sleep disturbance in AD patients. It is of interest to note that sleep is disrupted quite early in the disease process. In our study of early stage AD patients all were community dwelling and had relatively mild cognitive impairment (average MMS scores of 22.7). Despite this, significant increases in frequency and duration of awakening from sleep and reductions of SWS were observed in these patients. These findings indicate that when a patient is suspected of having AD it may be worthwhile as part of the evaluative and diagnostic process to caution both the patient and the patient's family that they might expect to see significant changes in sleep/wake patterns even though the patient's level of day-to-day functioning may still be high. It is also important to consider warning AD patients' families that as the disease progresses they should expect to see not only a worsening of nocturnal sleep quality but a breakdown of the circadian sleep/wake rhythm and an increase in daytime napping behavior by the patient. Families need to be encouraged to try and minimize the napping behavior of the patient in an effort to consolidate sleep into the night. This may have the effect of somewhat attenuating the amount of nocturnal disruption of sleep that accompanies progression of the disease.