Objective: To investigate depression at 12 months after traumatic brain injury (TBI) in older adults compared with younger adults. Design: Prospective longitudinal cohort study of persons with medically documented mild, moderate, and severe TBI at 12 months postinjury. Setting: Eighteen participating Level 1 trauma centers in the United States. Participants: Participants with TBI (N=1505) and primary outcome data at 12-month follow-up. Interventions: Not applicable. Main Outcome Measures: Patient Health Questionnaire-9 (PHQ-9). Results: PHQ-9 total scores were significantly lower for older adults (age≥65y; M=3.2) compared with younger adults (age<65y; M=5.0; B=−1.63, P<.001), indicating fewer depressive symptoms in older adults. Age did not interact with education, sex, race/ethnicity, psychiatric history, substance use, or Glasgow Coma Scale severity to affect PHQ-9 scores. Of the 29% of older adults who endorsed symptoms consistent with depression, 14% were classified as minor depression and 15% as major depression. The odds of older adults falling in the major depression vs no depression group were significantly lower (decreased by 56%) compared with younger adults (odds ratio=0.44, P=.001). Conclusions: At 12 months post-TBI, older adults endorse lower depressive symptoms than their younger counterparts and are less likely to experience major depression; however, over one-fourth of older adults endorsed symptoms consistent with depression, warranting evaluation and treatment.