In order to characterize the autonomic profile of syncopal children, we have studied heart rate variability (HRV) of 73 children, ages 11-18, with neurocardiogenic syncope and a positive outcome of head-up tilt testing (HUT).HRV was calculated over a 24-hour period for the time-domain indices (SDNN, SDANNi, SDNN, rMSSD, pNN50), and over 5-minute segments from night and day for frequency-domain indices (LF, HF, LF/HF). The obtained results were compared to reference values calculated for Polish children. 55% of the children had mixed response to HUT, 41% vasodepressor and 4% cardioinhibitory. Patients with syncope had significantly lower values of rMSSD and pNN50 in comparison to healthy children. Moreover, in the frequency-domain analysis they exhibited significantly higher LF and lower HF values. The day-night rhythm of HRV and the age-related changes of HRV were, however, similar in syncopal and healthy children. In addition to this, we found a significantly lower SDNN value in children with cardioinhibitory response during HUT in comparison to children with mixed response. We concluded that 1) based on HRV analysis children with neurocardiogenic syncope had alterations in basal autonomic balance, which indicated an increased sympathetic modulation in these patients, 2) syncopal children had adequate circadian rhythm of autonomic activity, 3) the changes of HRV indices with age in these groups are not altered in comparison to healthy children, 4) syncopal children may exhibit differences in HRV indices values depending on the kind of vasovagal response observed during HUT.