ABSTRACT: Uncertainties exist about the rates, predictors, and outcomes of major depressive disorder (MDD) among individuals with traumatic brain injury (TBI).To describe MDD-related rates, predictors, outcomes, and treatment during the first year after TBI.Cohort from June 2001 through March 2005 followed up by structured telephone interviews at months 1 through 6, 8, 10, and 12 (data collection ending February 2006).Harborview Medical Center, a level I trauma center in Seattle, Washington.Five hundred fifty-nine consecutively hospitalized adults with complicated mild to severe TBI.The Patient Health Questionnaire (PHQ) depression and anxiety modules were administered at each assessment and the European Quality of Life measure was given at 12 months.Two hundred ninety-seven of 559 patients (53.1%) met criteria for MDD at least once in the follow-up period. Point prevalences ranged between 31% at 1 month and 21% at 6 months. In a multivariate model, risk of MDD after TBI was associated with MDD at the time of injury (risk ratio [RR], 1.62; 95% confidence interval [CI], 1.37-1.91), history of MDD prior to injury (but not at the time of injury) (RR, 1.54; 95% CI, 1.31-1.82), age (RR, 0.61; 95% CI, 0.44-0.83 for > or = 60 years vs 18-29 years), and lifetime alcohol dependence (RR, 1.34; 95% CI, 1.14-1.57). Those with MDD were more likely to report comorbid anxiety disorders after TBI than those without MDD (60% vs 7%; RR, 8.77; 95% CI, 5.56-13.83). Only 44% of those with MDD received antidepressants or counseling. After adjusting for predictors of MDD, persons with MDD reported lower quality of life at 1 year compared with the nondepressed group.Among a cohort of patients hospitalized for TBI, 53.1% met criteria for MDD during the first year after TBI. Major depressive disorder was associated with history of MDD and was an independent predictor of poorer health-related quality of life.