Failed back surgery syndrome (FBSS), a chronic pain condition, is characterised by impaired autonomic tone with sympathetic prevalence and vagal withdrawal1. Spinal cord stimulation (SCS) is an approved pain relief treatment. However, it is currently unknown whether SCS is associated with improvements in autonomic function in individuals with FBSS. The objectives of this study were to measure autonomic function by means of heart rate variability (HRV), baroreflex sensitivity (BRS) and muscle sympathetic nerve activity (MSNA) in individuals with FBSS prior to undergoing SCS, and to evaluate change in autonomic function 3-6 months following SCS implantation. Autonomic function was measured in individuals with FBSS prior to, and 3-6 months following SCS. Measurements included: HRV, using statistical, Fourier and Poincaré analysis of the RR interval; BRS, using sequence method analysis of changes in heart rate in response to changes in systolic blood pressure; and the frequency (units/minute) and incidence (units/100 heart beats) of single MSNA units. Data were analysed by paired t-test and linear regression. Baseline autonomic measures were obtained in 14 participants (7 males) prior to SCS implant. Autonomic tone varied between participants: some had high sympathetic prevalence (as indexed by high LF/HF and MSNA frequency and incidence) and low vagal tone (indexed by low BRS), whilst others had values considered in the ‘normal’ range2. Ten participants (4 males) underwent further measurement 3-6 months following SCS implantation in which autonomic tone altered: there were trends towards reduced sympathetic prevalence (LF/HF and MSNA) and increases in vagal tone (BRS). Importantly, baseline measures of autonomic tone, particularly LF/HF (R2 = 0.669, p = 0.007) and BRS (R2 = 0.483, p = 0.038), significantly predicted change at 3-6 months post SCS implant. This means that patients with high LF/HF (reflecting sympathetic prevalence) and low BRS (reflecting low vagal tone) encountered greater improvements at 3-6 months follow-up. This is the first study combining HRV, BRS and MSNA to explore autonomic function in individuals with FBSS. Results revealed great heterogeneity in resting autonomic tone in this patient group, with some experiencing high sympathetic prevalence and low vagal tone. In addition, SCS tended to elicit a reduction in sympathetic prevalence, suggesting this may be an effective treatment for restoring autonomic balance in individuals with FBSS. Predicting autonomic response to SCS based on pre-implant BRS values is a key finding, suggesting that autonomic measurement might be a useful tool to identify those patients who have attenuated vagal control and heightened sympathetic outflow and who might benefit the most from SCS. With a greater sample, these findings could have important clinical impact, contributing to improving patient outcomes and safety.