Mild Traumatic Brain Injury (MTBI) is commonly categorized as when injury severity criteria are mild, but an intracranial abnormality is present on acute neuroimaging. The current study examined whether functional outcomes differed at one week post injury among older adult patients based on injury severity and acute computed tomography (CT) findings. Participants (≥55 years-old; = 173) presenting sequentially to the emergency department with a head injury were divided into three groups: complicated MTBI (positive CT; = 22), uncomplicated MTBI (negative CT; = 68), and mild head injury (unperformed CT, no documented loss of consciousness or post-traumatic amnesia; = 83). At one week post injury, the Modified Rankin Scale (i.e., difference score between pre/post-injury ratings; ∆MRS), Glasgow Outcome Scale-Extended (GOS-E), and Rivermead Post-Concussion Symptoms Questionnaire (RPQ) were administered. Participants differed on the ∆MRS and GOS-E, but not the RPQ. The complicated MTBI group had worse GOS-E ratings than the uncomplicated MTBI and mild head injury groups and worse ∆MRS than the mild head injury group, but the uncomplicated MTBI and mild head injury groups did not differ on either outcome. Macrostructural abnormality on CT was associated with worse functional outcome at one week post MTBI.