Previous research has reported altered autonomic function in individuals with Down syndrome (DS) at rest and in response to certain stimuli (i.e. isometric handgrip, aerobic exercise, and even tilt table testing). Yet, these observations have been made using group means in these previous studies. It is unknown if a subset of individuals with DS that have similar heart rate responses to a task would have similar responses in heart rate variability (HRV).PURPOSE: To compare autonomic function between individuals with and without DS, via HRV analyses, using upright tilt and matching subjects on change in HR to tilt.METHODS: Individuals with (25 ± 7 yrs; 30.4 ± 7.3 kg/m2) and without DS (27 ± 7 yrs; 24.7 ± 4.1 kg/m2) (n=15/group) were matched on their HR response to a 5 min head-up tilt at 80°. HRV was assessed in both the frequency (low frequency (LF), high frequency (HF), and LF/HF ratio) and time domains (Root mean square of successive differences (RMSSD)). A modified CM5 lead was used with data collected at 1000 Hz.RESULTS: Raw HRV data are presented below. As expected, tilt effects were observed for HR, HF, LF/HF ratio, and RMSSD in both groups, with no group differences (*p<0.05). However, individuals with DS exhibited a reduction in LF with no change in the control group (†p<0.05).CONCLUSION: Parasympathetic modulation appeared to be similar between individuals with DS and non-DS in response to orthostatic stress. LF, which contains both sympathetic and parasympathetic influences, responded quite differently to tilt in individuals with DS, suggesting possible autonomic dysfunction despite their normal HR response.