Objectives:To evaluate construct validity and responsiveness of the Brachial Assessment Tool (BrAT), a new patient-reported outcome measure for people with traumatic brachial plexus injury (BPI), and to compare it to the Disabilities of the Arm, Shoulder and Hand (DASH) and the Upper Extremity Functional Index (UEFI).Design:Cross-sectional study.Setting:Outpatient clinics.Participants:Adults (NZ29; age range, 20e69y) with confirmed traumatic BPI. Interventions: Participants completed the BrAT 3 times over an 18-month period together with 16 DASH activity items and the UEFI. Evaluations were undertaken of construct validity, known-groups validity, 1-way repeated analysis of variance, and effect size.Main Outcome Measures: BrAT, DASH, and UEFI. Results:The BrAT demonstrated a moderate to low correlation with the DASH activity items (<0.7) and a large correlation with the UEFI (>0.7). According to known-groups validity, only the BrAT was able to discriminate between people who stated they could use their hand versus those who were unable to use their hand to perform activities. All measures indicated a significant effect for time with the exception of BrAT subscale 1. The effect size was highest for the BrAT but lower than expected (BrAT, .52e.40; DASH, .15; UEFI, .36).Conclusions:These preliminary findings support the BrAT as a valid and responsive patient-reported outcome measure for adults with traumatic BPI. The BrAT activity items appear to be more targeted than the DASH or UEFI particularly for people with more severe BPI. The BrAT also appears to be measuring a different activity construct than the DASH and the UEFI. Further work is required to confirm these results with larger sample sizes.