Objective: The authors assessed the association of major depression with behavioral outcome following mild traumatic brain injury. Method: Consecutive patients with mild traumatic brain injury (N = 170) were assessed for major depression. Those with major depression were compared with those without on self-report measures of psychosocial dysfunction, psychological distress, and postconcussive symptoms in addition to examiner-rated neurobehavioral disturbance. Results: Major depression was seen in 15.3% (N = 26) of the subjects after traumatic brain injury, and these individuals showed subjective and objective evidence of poorer outcome. Conclusions: Major depression is associated with poor outcome across multiple domains. This study highlights the need for the early diagnosis and prompt treatment of major depression following mild traumatic brain injury.