The authors examine those factors that contributed to deterioration in social functioning, activities of daily living, or intellectual functioning during a 1-year period after traumatic brain injury (TBI). Fifty-two patients suffering an acute TBI were evaluated for existence and severity of mood disorders and impairment during their hospital stays and at 3-, 6-, and 12-month follow-up examinations. Patients whose scores on intellectual function, social function, or daily activities deteriorated during the 1-year period after trauma were considered to have a poor outcome. Eleven of 52 patients had a poor outcome in social function, which was associated with race, right-hemisphere lesions, intellectual impairment, and prolonged major depression. Seven of 52 patients had a poor outcome in daily activities, which was associated with a major depression of more than 6 months' duration and severity of Hamilton Depression Rating Scale scores. Eleven of these patients had a poor outcome in cognitive function, which was associated with cognitive impairment immediately after TBI. A major depression lasting more than 6 months was associated with deterioration of social functioning and activities of daily living during the 1-year period after TBI.