The majority of research into the assessment of mild traumatic brain injury (mTBI) has been focussed on the neuropsychological aspect of the injury, with neuropsychological tests forming the cornerstone of concussion management (Ross et al., 1987). The impact that mTBI has on the cerebrovascular system still remains relatively unclear (Wilberger et al., 2006, McCrory et al., 2009). With advancing techniques such as transcranical Doppler (TCD) assessing the impact on the cerebrovascular system has become a key aspect of recent research (Len and Neary, 2011). In the study we tested the hypothesis that cerebral function would show the greatest impairment i.e. reduced vasomotor reactivity in individuals who had the highest exposure to repetitive head trauma. Twelve currently active professional boxers aged 27 (mean) ± 4 (SD) years and 10 physically trained concussed individuals (28±8 years), with a history of knockouts 2±3 & 4±5 (respectively) were compared to 13 physically trained non-concussed individuals (22±3 years) and 11 sedentary individuals (25±5 years). Haemodynamic function was assessed following 3-minute of hypocapnea, with continuous recording of the middle cerebral artery velocity (MCAv), mean arterial pressure (MAP) and end-tidal partial pressure of carbon dioxide (PETCO2) Cerebrovascular resistance (CVR) was calculated as MAP/MCAv and cerebrovascular conductance (CVC) as MCAv/MAP. Vasomotor reactivity (VMR) was calculated as the percentage change in MCAv from hypocapnea to baseline/delta change in PETCO2. Data were analysed using a two-way repeated measures ANOVA and Bonferonni corrected independent and paired samples t-test. Significance was set at P<0.05. As shown in table 1, there was no visible impairment of the cerebrovascular function following the hypocapnea challenge across all groups. These findings demonstrate that cerebrovascular function remains preserved following a mTBI. By incorporating techniques such as TCD to assess cerebral function with neuropsychological tests will help improve further the understanding of the injury.