Patients with mild traumatic brain injury (mTBI) are at risk for post-concussion (PC) symptoms and post-traumatic stress disorder (PTSD). The co-occurrence of PC and PTSD symptoms after mTBI in relation to health-related quality of life (HRQoL), health care utilization, and return to work has not yet been investigated. PC and PTSD symptoms were measured six months post-TBI by respectively the Rivermead Post-Concussion Symptoms Questionnaire (RPQ) and the Post-Traumatic Stress Disorder Checklist for DSM-5 (PCL-5). Of the 1566 individuals after mTBI who met the inclusion criteria, 26.1% experienced PC symptoms (RPQ ≥16). Additionally, 9.8% experienced PTSD symptoms (PCL-5 ≥ 33), of which the vast majority (81%) also reported experiencing PC symptoms. Differences between patients with no/mild symptoms, with only PC, only PTSD, and both PC and PTSD symptoms in HRQoL, return to work, and rehabilitation were analyzed using logistic and linear regression analyses. Patients with PC and/or PTSD symptoms reported lower HRQoL, higher rates of rehabilitation, and lower return to work rates compared to patients with no/mild symptoms. Patients with both PC and PTSD symptoms reported significantly lower HRQoL (B = −2.73, CI = −4.65; −0.83, p < 0.001) compared to those with only PC symptoms, while there were no significant differences in their ongoing rehabilitation care (OR = 1.39, CI = 0.77–2.49, p = 0.272) and return to work rates (OR = 0.49, CI = 0.15–1.63, p = 0.246) at six months. These results underline the importance of the diagnosis and appropriate treatment of patients with mTBI, experiencing PC and/or PTSD symptoms.