Adenotonsillar hypertrophy is a major cause of obstructive sleep apnea (OSAS) in childhood. Increased respiratory effort associated with OSAS is accompanied by an increase in pulse transit time (PTT) but also mandibular movements (MMs) amplify with increased upper airway resistance. We compared dynamic changes in PTT and MMs using a magnetic distance sensor during polysomnography (PSG) in a pre-school child with severe OSAS before and after adenotonsillectomy. The results show that repetitive respiratory effort to overcome upper airway obstruction can be identified in children using MMs.