Chronic alveolar hypoventilation may present in an insidious fashion with nonspecific manifestations. The clinician should be aware of the potential for developing this condition in patients with certain thoracic and systemic diseases. Once chronic alveolar hypoventilation is confirmed with arterial blood gas analysis, a systematic evaluation can often point to the underlying etiology. As sleep in affected individuals is often associated with marked worsening of gas exchange and may also contribute to worsening daytime cardiopulmonary dysfunction, polysomnography is often indicated to determine the severity of nocturnal aberrations and to look for coexistent obstructive sleep apnea. Therapy of chronic alveolar hypoventilation often focuses on elimination of the nocturnal deterioration in gas exchange, and recent applications of noninvasive positive pressure ventilation during sleep have proven useful in the management of individuals with obesity-hypoventilation syndrome, restrictive thoracic disorders, neuromuscular diseases and central causes for hypoventilation. It is unclear whether wide-spread application of nocturnal ventilatory support to patients with chronic ventilatory failure due to chronic obstructive pulmonary disease is of long-term benefit.