Traumatic brain injury (TBI) is a major cause of death and disability and impairs health-related quality of life (HRQOL). Psychiatric disorders have been recognized as major components of TBI morbidity, yet few studies have addressed the relationship between these outcomes. Sample size, selection bias, and retrospective design, are methodological limitations for TBI-related psychiatric studies. For this study, 33 patients with severe TBI were evaluated prospectively regarding demographic, clinical, radiological, neurosurgical, laboratory, and psychosocial characteristics, as well as psychiatric manifestations and HRQOL, 18 months after hospitalization. Psychiatric manifestations were assessed using the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I), the Hospital Anxiety and Depression Scale (HADS), the Brief Psychiatric Rating Scale (BPRS), and the Apathy Evaluation Scale (AES). HRQOL was determined using the Medical Outcomes Study's 36-item Short-Form Health Survey (SF-36). Following TBI, a significant increase in the prevalence of major depressive disorder (MDD) and generalized anxiety disorder (p=0.02), and a significant decrease in the prevalence of alcohol and cannabinoid abuse (p=0.001) were observed. The most frequent psychiatric disorders following severe TBI were found to be MDD (30.3%), and personality changes (33.3%). In comparison to patients without personality changes, patients with personality changes experienced a decline in general health and impairments in physical and social functioning. Patients with MDD showed impairment in all SF-36 domains compared to non-depressed patients. This prospective TBI-related psychiatric study is the first to demonstrate a significant association between MDD, personality changes, and HRQOL, following severe TBI in a well-defined sample of patients.