To examine associations between pre-existing anxiety symptoms, and symptoms and cognitive functioning acutely following a suspected concussion. Nested case-control study. High schools in Maine, USA. 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). Immediate Post-Concussion Assessment and Cognitive Testing cognitive composite scores, PCSS total score, and symptom endorsement. 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. 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.