Disordered sleep and dementia are 2 neurologic issues that are found in many of the same patients, and may indeed interact. In dementia, degeneration of central sleep-wake mechanisms frequently leads to sleepiness and insomnia with sundowning. REM sleep behavior disorder can herald a synucleinopathy. In some cases, sleep apnea might result from degeneration of medullary respiratory centers. The treatment of sleepiness and insomnia with sundowning is not well-established, as many medications have risks that outweigh their benefits; however, REM sleep behavior disorder often responds to clonazepam, and continuous positive airway pressure therapy can improve cognition in some cases of obstructive sleep apnea. Drs. Im and Shim of the University of Iowa review these interactions, including recent updates on REM sleep behavior disorder.