To evaluate the reliability, validity and responsiveness of the High-level Mobility Assessment Tool (HiMAT) in children and adolescents with traumatic brain injury (TBI) and to compare the mobility skills of children with TBI to those of healthy peers.The mobility skills of 52 children with moderate and severe TBI (36 males; mean age = 12 years, range = 6-17) were assessed using the HiMAT and the Pediatric Evaluation of Disability Inventory (PEDI). Inter-rater reliability, re-test reliability and responsiveness of the HiMAT were evaluated in sub-groups by comparing results scored at several time-points. The HiMAT scores of children with TBI were compared with those of a healthy comparative cohort.The HiMAT demonstrated excellent inter-rater reliability (ICC = 0.93), re-test reliability (ICC = 0.98) and responsiveness to change (p = 0.002). The PEDI demonstrated a ceiling effect in mobility assessment of ambulant children with TBI. The HiMAT scores of children with TBI were lower than those of their healthy peers (p < 0.001).The HiMAT is a reliable, valid and sensitive measure of high-level mobility skills following childhood TBI. The high-level mobility skills of children with TBI are less proficient than their peers.