Testosterone is thought to play a role in the pathogenesis of obstructive sleep apnea (OSA), but the mechanism is unclear. We present a case in which testosterone administration induced or exacerbated OSA in a 13-year-old male. We demonstrated that exacerbation of OSA by testosterone was associated with an increase in upper airway collapsibility during sleep, and that this improved after cessation of hormone administration. Our data strongly suggest that the mechanism by which testosterone administration may induce or exacerbate OSA is through an influence on neuromuscular control of upper airway patency during sleep.