Background: High velocity thrust (HVT) cervical techniques have been associated with serious vertebral artery (VA) trauma. Despite numerous studies, the nature of this association is uncertain. Previous studies have failed to demonstrate haemodynamic effects on the VA in simulated pre-thrust positions. No study has investigated haemodynamic affects during or immediately following HVT, nor sufficiently controlled for the influence of the thrust., Objectives: To investigate the immediate effects of HVT of the atlanto-axial joint upon haemodynamics in the sub-occipital portion of the vertebral artery (VA3)., Design: Randomized Controlled Trial., Method: Twenty-three healthy participants (14 women, 9 men; mean age 40, range 27-69 years of age) were randomly assigned to two groups: an intervention group (MANIP, n = 11) received HVT to the atlanto-axial segment whilst a control group (CG, n = 12) was held in the pre-manipulative hold position. Colour-flow Doppler ultrasound was used to measure VA3 haemodynamics. Primary outcome measures were peak systolic (PSV) and end diastolic velocities (EDV) of three cardiac cycles measured at neutral (N1), pre-HVT (PreMH), post-HVT (PostMH), post-HVT-neutral (N2) positions., Results: Test-retest reliability for the Doppler measures demonstrated intra-class correlation coefficient (ICC) of 0.99 (95% CI 0.98-1.0) for PSV and 0.91 (95% CI 0.84-0.96) for EDV. Visually, EDV were lower in the MANIP group than in the CONTROL group across the four measurements. However, there were no significantly different changes (at p ≤ 0.01) between the MANIP and CONTROL groups for any measurement variable., Conclusions: HVT to the atlanto-axial joint segment does not affect the haemodynamics of the sub-occipital portion of the vertebral artery during or immediately following HVT in healthy subjects., (Copyright © 2015 Elsevier Ltd. All rights reserved.)