Objective: To examine minor as well as major depression at 1 year posttraumatic brain injury (TBI), with particular attention to the contribution of depression severity to levels of societal participation. Design: Observational prospective study with a 2-wave longitudinal component. Setting: Inpatient rehabilitation centers, with 1-year follow up conducted primarily by telephone. Participants: Persons with TBI (N=1570) enrolled in the TBI Model System database and followed up at 1-year postinjury. Interventions: Not applicable. Main Outcome Measures: FIM, Patient Health Questionnaire-9, Participation Assessment with Recombined Tools-Objective, Glasgow Outcome Scale-Extended, and the Satisfaction With Life Scale. Results: Twenty-two percent of the sample reported minor depression, and 26% reported major depression at 1-year post-TBI. Both levels of depression were associated with sex (women), age (younger), preinjury mental health treatment and substance abuse, and cause of injury (intentional). There was a monotonic dose-response relationship between severity of depression and all 1-year outcomes studied, including level of cognitive and physical disability, global outcome, and satisfaction with life. With other predictors controlled, depression severity remained significantly associated with the level of societal participation at 1-year post-TBI. Conclusions: Minor depression may be as common as major depression after TBI and should be taken seriously for its association to negative outcomes related to participation and quality of life. Findings suggest that, as in other populations, minor and major depression are not separate entities, but exist on a continuum. Further research should determine whether people with TBI traverse between the 2 diagnoses as in other patient groups. © 2011 American Congress of Rehabilitation Medicine.