Objective:The Sports Concussion Assessment Tool 3 (SCAT3) Symptom Evaluation (SE) is used in the emergency department (ED). This study aimed to examine the effects of psychiatric history on the SCAT3 SE symptom severity score (SSS). Setting: Three US EDs. Participants: A total of 272 ED patients with suspected concussion. Design: Prospective, nonrandomized, nonblinded study. The SCAT3 SE SSS, demographic data, medical information, and self-reported psychiatric history were obtained from patients by clinical research staff when they presented to the ED seeking standard clinical care. Concussion diagnoses were determined following a comprehensive assessment by an ED physician trained in managing concussions and adjudicated by supervising physicians. Main Measures: The primary outcome measure was SSS. The association between SSS, self-reported psychiatric disease, and concussion diagnosis was analyzed using multivariable linear regression. Results: 68.4% of subjects were diagnosed with a concussion. After controlling for age, sex, race, history of previous concussion, and interval from injury to ED presentation, self-reported psychiatric history (adjusted regression coefficient (β a ): 16.9; confidence interval [CI]: 10.1, 23.6), and concussion diagnosis (β a : 21.7; CI: 14.2, 29.2) were both independently associated with a significant increase in SSS. Subjects with a history of concussion had a significantly higher SSS (β a : 9.1; CI: 1.8, 16.5). Interval from injury to ED presentation was also associated with a significant increase in SSS (β a : 1.6 per 6-hour increase; CI: 0.4, 2.8). Conclusion: Our findings demonstrate that a history of preexisting psychiatric disease, as self-reported by patients with a suspected concussion treated in the ED, is independently associated with significantly higher scores on the SCAT3 SE. This suggests that a history of psychiatric illness may need to be accounted for when the SCAT3 SE is used in the ED for the assessment of concussion.