Forty-one children and adolescents with a history of breathing difficulty during sleep and morbid obesity, defined as greater than 150% ideal body weight, underwent polysomnography to determine the incidence of sleep-associated breathing disorders. Seventeen patients also performed pulmonary function testing. The mean patient age was 10.3 +/- 4.4 (SD) years, and mean percent of ideal body weight was 208 +/- 42.2. A sleep history questionnaire showed that all patients snored, but frank apnea was reported in only 32%. The pulmonary function tests showed 18% (3/17) with a restrictive defect and 47% (8/17) with obstructive changes. The polysomnograms in 37% (15/41) of the patients were abnormal because of apnea, hypopnea, excessive arousals, or abnormalities in gas exchange. Multiple regression analysis demonstrated no significant association between weight, age, or gender and any physiologic measure on the polysomnogram. Most of the abnormal polysomnograms (13/15) were mildly abnormal, but two showed sufficiently severe abnormalities to require clinical intervention. We conclude that children and adolescents with morbid obesity are at risk for sleep-associated breathing disorders; their polysomnographic abnormalities are usually mild but rarely may be severe enough to require clinical intervention.