Sleep apnea is a common disorder in the elderly and is characterized by recurrent apneas which are associated with periodic oxyhemoglobin desaturations and arousals from sleep. In more severely affected individuals, it may result in marked sleep fragmentation, alterations in daytime function, and increased cardiovascular morbidity and mortality. In milder cases, however, physiologic abnormalities which are recognized may have a questionable impact on morbidity and mortality. Therefore, the decision to treat this disorder rests on accurately assessing the severity of physiologic disturbances in sleep and in breathing, and depends on determining whether daytime function is impaired.