Sleep-disordered breathing occurs in approximately 2% to 4% of the adult population and includes conditions in which patients stop breathing completely (apnea) or have marked reductions in airflow (hypopnea) during sleep. Typical symptoms of sleep apnea include snoring, restless sleep, excessive daytime somnolence, nocturnal enuresis, irritability, depression, memory deficits, inability to concentrate, and decreased alertness. The clinically relevant outcomes of these symptoms include impairment in work efficiency, increased automobile accident rates, and decrements in quality of life. Treatment of sleep apnea, primarily with continuous positive airway pressure, reduces sleepiness and improves mood disturbances, neurocognition, and performance. Traditional measurements of sleep apnea severity do not correlate well with current tests and scales that are used to quantify alterations in alertness, performance, quality of life, or sleepiness. A disease-specific quality of life scale has been developed following patient and physician interviews and literature reviews. The Calgary Sleep Apnea Quality of Life Index is expected to capture aspects of quality of life important to sleep apnea patients, such as cognitive function, performance, and mood, that could be improved with appropriate treatment of sleep-disordered breathing. (J Allergy Clin Immunol 1997;99:S750-6.)