ObjectivesHeadgear use is a controversial issue in girls’ lacrosse. We compared concussion rates among high school lacrosse players in an American state with a headgear mandate (HM) to states without an HM.MethodsParticipants included high schools with girls’ lacrosse programmes in the USA. Certified athletic trainers reported athlete exposure (AE) and injury data via the National Athletic Treatment, Injury and Outcomes Network during the 2019–2021 seasons. The HM cohort was inclusive of high schools from the state of Florida, which mandates the use of ASTM standard F3137 headgear, while the non-HM (NHM) cohort was inclusive of high schools in 31 states without a state-wide HM. Incidence rate ratios (IRRs) and 95% CIs were calculated.Results141 concussions (HM: 25; NHM: 116) and 357 225 AEs were reported (HM: 91 074 AEs; NHM: 266 151 AEs) across all games and practices for 289 total school seasons (HM: 96; NHM: 193). Overall, the concussion injury rate per 1000 AEs was higher in the NHM cohort (0.44) than the HM cohort (0.27) (IRR=1.59, 95% CI: 1.03 to 2.45). The IRR was higher for the NHM cohort during games (1.74, 95% CI: 1.00 to 3.02) but not for practices (1.42, 95% CI: 0.71 to 2.83).ConclusionsThese findings suggest a statewide HM for high school girls’ lacrosse is associated with a lower concussion rate than playing in a state without an HM. Statewide mandates requiring ASTM standard F3137 headgear should be considered to reduce the risk of concussion.