Bilateral vocal cord abductor paralysis (VCAP) is frequently associated with multiple system atrophy (MSA) and the early clinical manifestation of VCAP is nocturnal inspiratory stridor simulating heavy snoring observed in patients with obstructive sleep apnea syndrome. We examined six MSA patients with nocturnal stridor and four disease controls including sleep apnea syndrome. Vocal cord movements were analyzed by laryngofiberscopy during both wakefulness and sleep induced by intravenous administration of diazepam. The results were as follows: First, the stenotic portion in the upper airway tract was the larynx (the vocal cords) in MSA patients with stridor, while the soft palate or the pharynx in the disease controls. Second, in the MSA patients, while awake-laryngofiberscopy showed abduction restriction suggestive of VCAP in only one of the six patients, sleep-laryngofiberscopy showed obvious paradoxical movement of the vocal cord in all the rests, where the vocal cords abducted in expiration and adducted in inspiration. In addition, there were two patterns in the inspiratory vocal cord position during sleep: one pattern where vocal glottis was still opening at the posterior one-third area and the other pattern where vocal glottis was almost completely closed through total length of the cords. Tracheostomy should be considered in the latter stage of VCAP.