Autism Spectrum Disorders (ASD) is a group of neurodevelopmental disorders often manifested by social and behavioral deficiencies. Autonomic dysfunction is frequently reported in the autistic population but the mechanisms remain largely unknown. We aimed to characterize the cardiac autonomic profile of children with autism during a head-up tilt test. Thirty-nine male children were recruited: 19 controls (9.9 ± 1.6 years) and 20 children with ASD without intellectual disability (10.7 ± 1.2 years). Each child underwent a head-up tilt test on a motorized tilt table. After a 10 min resting period in the supine position, subjects were tilted head-up to 70° on the table for 10 min. Heart rate and blood pressure variabilities were continuously recorded using non-invasive Nexfin monitoring. The head-up tilt test significantly altered heart rate variability (p < 0.001 for both groups) and greater parasympathetic responses were found in the ASD group compared to controls (p < 0.05). In the supine position baroreflex sensitivity was higher in children with ASD than in the controls (p < 0.05) and significantly decreased during the tilt test in the ASD group, but not in controls. Our results showed that children with ASD did not have clinical signs of dysautonomia in response to a head-up tilt test. However, in children with ASD higher parasympathetic responses with the same sympathetic modulations during orthostatic stress suggest parasympathetic dominance in this population.