OBJECTIVE The aim of the study is to characterize changes in circulating proteasome (c-proteasome) activity following mild traumatic brain injury in children. METHODS Fifty children managed at the Department of Pediatric Surgery because of concussion-mild head injury was randomly included into the study. The children were aged 11 months to 17 years (median = 10.07 + -1.91 years). Plasma proteasome activity was assessed using Suc-Leu-Leu-Val-Tyr-AMC peptide substrate, 2-6 h, 12-16 h, and 2 days after injury. Twenty healthy children admitted for planned inguinal hernia repair served as controls. RESULTS Statistically significant elevation of plasma c-proteasome activity was noted in children with mild head injury 2-6 h, 12-16 h, and 2 days after the injury. CONCLUSIONS Authors observed a statistically significant upward trend in the c-proteasome activity between 2-6 and 12-16 h after the mild head injury, consistent with the onset of the symptoms of cerebral concussion and a downward trend in the c-proteasome activity in the plasma of children with mild head injury between 12-16 h and on the second day after the injury, consistent with the resolving of the symptoms of cerebral concussion. Further studies are needed to demonstrate that the proteasome activity could be a prognostic factor, which can help in further diagnostic and therapeutic decisions in patients with head injury.