Aggression after traumatic brain injury (TBI) is common but not well defined. Sixty-seven participants with first-time TBI were evaluated for aggression within 3 months of injury. The prevalence of aggression was found to be 28.4%, predominantly verbal aggression. Post-TBI aggression was associated with new-onset major depression (p=0.02), poorer social functioning (p=0.04), and increased dependency in activities of daily living (p=0.03), but not with a history of substance abuse or adult/childhood behavioral problems. Implications of the study include early screening for aggression, evaluation for depression, and consideration of psychosocial support in aggressive patients.