It is well established that traumatic brain injury (TBI) is associated with the development of psychiatric disorders. However, the impact of psychiatric disorders on TBI outcome is less well understood. We examined the outcomes of patients who experienced a traumatic subdural hemorrhage and whether a comorbid psychiatric disorder was associated with a change in outcome. A retrospective observational study was performed in the California Office of Statewide Health Planning and Development (OSHPD) and the Nationwide Inpatient Sample (NIS). Patients hospitalized for acute subdural hemorrhage were identified using International Classification of Diseases, Ninth Revision (ICD-9) diagnosis codes. Patients with coexisting psychiatric diagnoses were identified. Outcomes studied included mortality and adverse discharge disposition. In OSPHD, diagnoses of depression (OR=0.64, p<0.001), bipolar disorder (OR=0.45, p<0.05), and anxiety (OR=0.37, p<0.001) were associated with reduced mortality during hospitalization for TBI, with a trend toward psychosis (OR=0.56, p=0.08). Schizophrenia had no effect. Diagnoses of psychosis (OR=2.12, p<0.001) and schizophrenia (OR=2.60, p<0.001) were associated with increased adverse discharge. Depression and bipolar disorder had no effect, and anxiety was associated with reduced adverse discharge (OR=0.73, p=0.01). Results were confirmed using the NIS. Analysis revealed novel associations between coexisting psychiatric diagnoses and TBI outcomes, with some subgroups having decreased mortality and increased adverse discharge. Potential mechanisms include pharmacological effects of frequently prescribed psychiatric medications, the pathophysiology of individual psychiatric disorders, or under-coding of psychiatric illness in the most severely injured patients. Because pharmacological mechanisms, if validated, might lead to improved outcome in TBI patients, further studies may provide significant public health benefit.