Objectives: After mild traumatic brain injury (mTBI), psychological factors can contribute to persisting post-concussion symptoms (PCS). Consistent with constructive theories of memory, negative expectations for increased symptoms after mTBI may contribute to misattributing symptoms to the mTBI and underestimating pre-injury symptoms, called the “good old days’ bias” (Gunstad & Suhr, 2001). The good old days’ bias is not thought to be a general retrospective recall bias but studies to date have largely not controlled for normative memory processes including those that lead to a biased, more positive recall of the past. Therefore, the current study examines whether there is a good old days’ bias after mTBI above and beyond normal memory biases. This study also examines how soon after mTBI the good old days’ bias affects recall of pre-injury symptoms in the first month after mTBI in adolescents as well as whether the good old days’ bias causes pre-injury symptom severity to be underestimated or if symptoms are entirely forgotten. Finally, the clinical significance of symptom recall biases is investigated. Method: The sample is 42 adolescents who sustained an mTBI (ages 13-18 years; 24 males) and 42 uninjured adolescents (ages 13-18 years; 24 males, ). The mTBI group rated current and retrospective post-concussion symptom ratings within one week and again, at one month, post-injury. The control group rated current and retrospective post-concussion symptoms at baseline and one month later. Cross-sectional and longitudinal comparisons using non-parametric statistical tests were used. Results: Wilcoxon signed-rank tests showed that, by one month post-mTBI, adolescents report fewer total, physical, and emotional pre-injury symptoms than they had reported within one week of their concussion. The control group did not demonstrate this good old days’ bias. There were no between-group differences in retrospective PCS ratings at either time point. Chi-square analyses found that the mTBI group was as likely as the control group to recall “no” pre-injury/past symptoms one month post-injury after having initially reported some pre-injury symptoms. Only four more adolescents were classified as “recovered” if their one-month PCS ratings were compared with pre-injury PCS ratings made within 1-week post-concussion rather than pre-injury ratings from 1-month post-injury. Discussion: There was mixed evidence for a good old days’ bias by one month post-concussion. This bias was not demonstrated in healthy adolescents, suggesting that the good old days’ bias is found specifically after concussion. During the acute post-injury period, the good old days’ bias may only be apparent by studying changes in concussed individuals’ own PCS ratings. The good old days’ bias leads to underestimating the severity of pre-injury symptoms rather than forgetting them entirely. The good old days’ bias does not greatly affect symptom recovery tracking by one month post-concussion. Future studies should directly examine expectations about concussion and their effect on current and retrospective symptom reporting. / Graduate / 2019-07-10