Sleep-disordered breathing (SDB) is underdiagnosed in infants and children. In addition to causing physical ailments that range from failure to thrive to cor pulmonale, SDB is often an unrecognized cause of failure in school or of behavioral disorders. Diagnosis of SDB requires a careful and detailed history and physical examination. Polysomnography is required to determine the nature of the problems, the magnitude of the physiologic disturbance, and, ultimately, the significance of the problem for the child. Earlier recognition, accurate diagnosis, and appropriate treatment should alleviate much of the childhood morbidity associated with these conditions.