These clinical guidelines, which have been reviewed and approved by the Board of Directors of the American Sleep Disorders Association, provide recommendations for the practice of sleep medicine in North America regarding the indications for polysomnography in the diagnosis of sleep disorders. Diagnostic categories that are considered include the following: sleep-related breathing disorders; neuromuscular disorders and sleep-related symptoms; chronic lung disease; narcolepsy; parasomnias; sleep-related epilepsy; restless legs syndrome; periodic limb movement disorder; depression with insomnia; and circadian rhythm sleep disorders. Whenever possible, conclusions are based on evidence from review of the literature. Where scientific data are absent, insufficient, or inconclusive, recommendations are based on consensus of opinion. The Standards of Practice Committee of the American Sleep Disorders Association appointed a task force to review the topic, the indications for polysomnography and related procedures. Based on the review and on consultation with specialists, the subsequent recommendations were developed by the Standards of Practice Committee and approved by the Board of Directors of the American Sleep Disorders Association. Polysomnography is routinely indicated for the diagnosis of sleep-related breathing disorders; for continuous positive airway pressure (CPAP) titration in patients with sleep-related breathing disorders; for documenting the presence of obstructive sleep apnea in patients prior to laser-assisted uvulopalatopharyngoplasty; for the assessment of treatment results in some cases; with a multiple sleep latency test in the evaluation of suspected narcolepsy; in evaluating sleep-related behaviors that are violent or otherwise potentially injurious to the patient or others; and in certain atypical or unusual parasomnias. Polysomnography may be indicated in patients with neuromuscular disorders and sleep-related symptoms; to assist in with the diagnosis of paroxysmal arousals or other sleep disruptions thought to be seizure-related; in a presumed parasomnia or sleep-related epilepsy that does not respond to conventional therapy; or when there is a strong clinical suspicion of periodic limb movement disorder. Polysomnography is not routinely indicated to diagnose chronic lung disease; in cases of typical, uncomplicated, and noninjurious parasomnias when the diagnosis is clearly delineated; for patients with epilepsy who have no specific complaints consistent with a sleep disorder; to diagnose or treat restless legs syndrome; for the diagnosis of circadian rhythm sleep disorders; or to establish a diagnosis of depression.