Background: Although patients with myelomeningocele and the Chiari II malformation are known to have sleep apnea and respiratory control deficits, the prevalence, types, severities, and associations of sleep-disordered breathing (SDB) have not been adequately defined. Methods: A cross-sectional study of our myelomeningocele clinic population was undertaken to correlate polysomnographic results with historical data and findings from magnetic resonance imaging of the Chiari malformation, pulmonary function results, and nocturnal pulse oximetry. Results: A questionnaire survey of symptoms was available for 107/109 children (98% of the clinic) and 83 patients agreed to overnight polysomnography. Breathing during sleep was classified as normal in 31 cases(37%), mildly abnormal in 35 cases (42%) and moderately/severely abnormal in 17 cases (20%). Amongst the 17 patients with moderately/severely abnormal SDB, 12 patients had predominantly central apneas and 5 had predominantly obstructive apnea. Failure of obstructive SDB to resolve after adenotonsillectomy in 4 patients suggested abnormal control of pharyngeal airway patency during sleep. Patients with a thoracic or thoracolumbar myelomeningocele, those who had previously had a posterior fossa decompression operation, those with more severe brainstem malformations, and those with pulmonary function abnormalities were more likely to have moderately/severely abnormal SDB: relative risks (95% confidence intervals) 9.2 (2.9-29.3), 3.5(1.3-8.9), 3.0(0.9-10.5), and 11.6(1.6-81.3), respectively. Nocturnal pulse oximetry accurately predicted moderately/severely abnormal SDB with a sensitivity of 100%. Conclusions: The pathogenesis of SDB seen in patients with myelomeningocele involves the functional level of the spinal lesions, congenital and acquired brainstem abnormalities, pulmonary function abnormalities, disorders of upper airway maintenance, and sleep state. Polysomnography and nocturnal pulse oximetry should be performed in high risk patients to detect and classify SDB.