Adequate sleep, in terms of both quantity and quality, is an essential component of any overall health program. Sleep deprivation has serious deleterious effects on any subject, regardless of species. The most obvious and well-documented adverse effects of sleep deprivation are focused on cognitive function, cardiopulmonary function, and the immune system. Despite these deleterious effects of sleep deprivation, even on healthy subjects, intensive care patients are rarely permitted sufficient natural sleep. The causes of sleep disturbance in the intensive care unit involve factors related to the underlying clinical condition, those due to the various drugs required to provide treatment and comfort, and those related to the environment and processes of care in the intensive care unit. Only through a comprehensive approach to intensive care can an environment that promotes sleep and revitalization be constructed and maintained.