Many patients with mild traumatic brain injury (MTBI) concurrently sustain extracranial injuries; however, little is known about the impact of these additional injuries on outcome. We assessed the impact of additional injuries on the severity of postconcussional symptoms (PCS) and functional outcome 6 months post-injury. A questionnaire (including the Rivermead Post-Concussion Questionnaire and SF-36) was sent to consecutive MTBI patients (hospital admission Glasgow Coma Score 13-15; age range 18-60 years) admitted to the emergency department of a level-I trauma center, and, to serve as a baseline for PCS, a control group of minor-injury patients (ankle or wrist distortion). Of the 299 MTBI respondents (response rate 52%), 89 had suffered additional injuries (mean Injury Severity Score [ISS] of 14.5 +/- 7.4). After 6 months, 44% of the patients with additional injuries were still in some form of treatment, compared to 14% of patients with isolated MTBI and 5% of the controls. Compared to patients with isolated injury, MTBI patients with additional injuries had resumed work less frequently and reported more limitations in physical functioning. Overall, they did not report higher levels of PCS, despite somewhat more severe head injury. Regardless of the presence of additional injuries, patients that were still in treatment reported significantly more severe PCS, with highest rates in patients with isolated MTBI. In conclusion, many patients with additional extracranial injuries are still in the process of recovery at 6 months after injury. However, despite more severe impact to the head and inferior functional outcomes, these patients do not report more severe PCS.