Sleep, cognition, and behavior have all been observed to change as a consequence of the normal aging process as well as the pathological processes that occur in Alzheimer's disease (AD). In the early stages of AD, it is quite possible that sleep disturbances that are occurring as a result of normal aging also exacerbate the cognitive and behavioral symptoms of AD. As the disease progresses, sleep disturbances associated with the pathological neurodegeneration characteristic of AD emerge, with further behavioral and cognitive consequences. Sleep disturbances in AD have been noted using many subjective and objective measures, and these sleep disturbances increase with the severity of dementia. Evidence of phase disturbance of the circadian rhythm in patients with AD comes from many different studies using several methods. A recent study demonstrated that treatment compliance with continuous positive airway pressure device (CPAP) could be achieved in patients with possible or probable AD.