BACKGROUND: Airway obstruction occurs in anesthetized children with obstructive sleep apnea syndrome (OSAS). The inspiratory attempts against the occluded airway lead to an increased sympathetic activity. Heart rate variability (HRV) analysis provides information about the autonomic nervous system. The low-frequency component/high-frequency component ratio of HRV is considered to be an index of sympatho-parasympathetic balance. METHODS: We investigated the effects of general anesthesia, the neutral neck position, and jaw thrust in the supine and lateral positions on HRV in 20 children (aged 3-9 yr), with OSAS. HRV was recorded before and after anesthesia induction, at the neutral neck position and with jaw thrust maneuver in the supine and lateral positions with the patients breathing 5% sevoflurane. RESULTS: General anesthesia with the patient in the neutral neck position increased airway obstruction. The patients\' stridor scores improved with the airway maneuver of jaw thrust and lateral position. The low-frequency component/high-frequency component ratio and heart rate increased at the postinduction measurement and reached the highest value with the patient in the neutral neck position. The values significantly decreased with the jaw thrust maneuver and with the patient in the supine and lateral positions. Ultra-short-term entropy of HRV decreased after anesthetic induction and reached the lowest value with the patient in the neutral neck position. The values increased during jaw thrust and with patients in the supine and lateral positions. CONCLUSIONS: Changes of HRV induced by inhaled anesthesia, jaw thrust, and lateral positioning procedures corresponded to changes in the stridor score of children with OSAS.