Patients diagnosed with major depression following mild TBI will be treated for ten weeks with the antidepressant drug citalopram. Those who respond, meaning that the symptoms of depression have lessened significantly, will be randomly assigned to either continue taking the citalopram for one year or to take a placebo for one year. Every four weeks, for an additional forty weeks, patients will be assessed for relapse of depression. This study will have a double-blind design, meaning that neither patient nor clinician know whether citalopram or placebo is being administered.