Some infants with myelomeningocele, hydrocephalus, and Arnold-Chiari malformation have symptomatic apnea or hypoventilation. The incidence of abnormalities of the ventilatory pattern during sleep in asymptomatic infants with myelomeningocele is not known. Therefore we performed overnight pneumograms (recordings of ventilatory pattern and electrocardiogram) in 18 asymptomatic infants with myelomeningocele and compared them with pneumograms from 64 control infants. Infants with myelomeningocele had longer total sleep time (596 +/- 16 minutes vs 536 +/- 10 minutes, P less than 0.005), longer episodes of longest apnea (12.6 +/- 0.8 seconds vs 8.1 +/- 0.3 seconds, P less than 0.001), greater total duration of apnea greater than or equal to 6 seconds as percent total sleep time (1.02% +/- 0.18% vs 0.23% +/- 0.03%, P less than 0.001), and lower mean heart rates (120 +/- 5 vs 145 +/- 5, P less than 0.001) than did control infants. No abnormal bradycardia was observed in either group. Thirteen (72%) of 18 infants with myelomeningocele had abnormal pneumograms, compared with 4 (6%) of 64 control infants (P less than 0.0005). We conclude that asymptomatic infants with myelomeningocele have a high incidence of ventilatory pattern abnormalities during sleep.