We report two children with severe sleep-disordered breathing associated with Klippel-Feil sequence. In both patients, minor vertebral anomalies were associated with a major hindbrain anomaly. In one child, the Klippel-Feil sequence had been diagnosed previously, but the hindbrain anomaly was not recognized. Two years later, this child developed fatal obstructive sleep apnea. In the other child, neither the Klippel-Feil sequence nor hindbrain anomaly had been identified before the child's presentation with sleep-disordered breathing characterized by bradypnea and stridor. Because many of the complications of hindbrain anomalies may be amenable to neurosurgical treatment, we recommend that patients with Klippel-Feil sequence be followed for the development of sleep-disordered breathing. Sleep complaints need prompt evaluation with polysomnography, whereas neurologic signs require imaging with attention to the cervicomedullary junction. Unsuspected CNS disorders must be considered in children who present with stridor or serious respiratory disturbances during sleep.