Objective: To examine associations between pre-existing anxiety symptoms, and symptoms and cognitive functioning acutely following a suspected concussion. Design: Nested case–control study. Setting: High schools in Maine, USA. Participants: Participants were identified from a dataset of 46 920 student athletes ages 13 to 18 who received baseline preseason testing. A subset of 4732 underwent testing following a suspected concussion. Of those, 517 were assessed within 72 hours after their suspected concussion and met other inclusion criteria. Nineteen injured athletes endorsed anxiety-like symptoms on the Post-Concussion Symptom Scale (PCSS) during baseline testing and were placed in the high anxiety group. Each athlete was matched to 2 injured athletes who did not endorse high levels of anxiety-like symptoms (N = 57). Main Outcome Measures: Immediate Post-Concussion Assessment and Cognitive Testing cognitive composite scores, PCSS total score, and symptom endorsement. Results: Cognitive composite scores were similar between groups across testing times ( = 0.004-0.032). The high anxiety group endorsed a greater number of symptoms than the low anxiety group ( = 0.452) and rated symptoms as more severe ( = 0.555) across testing times. Using a modified symptom score that excluded anxiety-like symptoms, a mixed analysis of variance indicated a group by injury interaction ( = 0.079); the high anxiety group reported greater increases in overall symptom severity following injury. Conclusions: Adolescent athletes who have an anxious profile at baseline are likely to experience greater symptom burden following injury. Consideration of pre-injury anxiety may inform clinical concussion management by tailoring intervention strategies (eg, incorporating mental health treatments) to facilitate concussion recovery. Corresponding Author: Magdalena Wojtowicz, PhD, Department of Psychology, York University, 4700 Keele St, Toronto, ON M3J 1P0, Canada (firstname.lastname@example.org). P. D. Berkner acknowledges funding for the Maine Concussion Management Initiative from the Goldfarb Center for Public Policy and Civic Engagement/Colby College and the Bill and Joan Alfond Foundation. G. L. Iverson acknowledges support from the National Football League for a program of research entitled “The Spectrum of Concussion: Predictors of Clinical Recovery, Treatment and Rehabilitation, and Possible Long-Term Effects,” and unrestricted philanthropic support from ImPACT Applications, Inc., the Mooney-Reed Charitable Foundation, Boston Bolts, Heinz Family Foundation, National Rugby League, and the Spaulding Research Institute. M. Wojtowicz acknowledges funding from Natural Sciences and Engineering Research Council of Canada. D. P. Terry is a consultant for REACT Neuro Inc. G. L. Iverson has received research funding from several test publishing companies, including ImPACT Applications, Inc., CNS Vital Signs, and Psychological Assessment Resources (PAR, Inc), and the National Football League. He serves as a scientific advisor for Sway Operations, LLC, Highmark, Inc., and NanoDx. He has received salary support from the Harvard Integrated Program to Protect and Improve the Health of National Football League Players Association Members. The remaining authors report no conflicts of interest. Received November 30, 2020 Accepted July 08, 2021 Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.