We report on a patient with mental retardation and chronic hypercapnic respiratory failure who was found to have severe central apnea and periodic breathing while undergoing an evaluation of low oxygen saturation during wakefulness at rest. Magnetic resonance imaging of the brain, which was performed to uncover potential causes for the central sleep apnea, revealed a "molar tooth sign" consistent with the diagnosis of Joubert syndrome. Joubert syndrome-related disorders are autosomal-recessive disorders characterized by diffuse hypotonia, developmental delay, abnormal respiratory patterns, and the pathognomonic neuroradiologic finding of a molar tooth sign. Adaptive servoventilation failed to correct the central apneas or the periodic breathing. Treatment with bilevel positive airway pressure in S/T mode led to resolution of the central events, improvement in sleep quality, and normalization of the oxygen saturation during wakefulness.