Objective: To evaluate how demographics, measures of injury severity, and acute care complications relate to sitting and standing balance in patients with traumatic brain injury (TBI). Design: Multicenter analysis of consecutive admissions to designated TBI Model Systems of Care (TBIMS). Setting: Ten National Institute for Disability and Rehabilitation Research TBI Model System centers for coordinated acute and rehabilitation care. Participants: 908 adults with TBI were included in the study. Main Outcome Measures: Sitting and standing balance were assessed within 72 hours of admission to inpatient rehabilitation. Results: Age less than 50 years had a significant association with normal sitting and standing balance (P = .001 and .05, respectively). Measures of severity of traumatic brain injury, including admission Glasgow Coma Score, length of posttraumatic amnesia (PTA), length of coma, and acute care length of stay were each significantly related to impaired sitting and standing balance ratings (P < .01). Initial abnormalities in pupillary response had a significant relationship with impairment of sitting (P = .009) but not standing balance. Incidence of respiratory failure, pneumonia, soft tissue infections, and urinary tract infections were all related to impaired sitting balance (P < .01). Presence of intracranial hemorrhages did not have a significant relationship with either sitting or standing balance. Intracranial compression had a significant relationship with standing (P = .05) but not sitting balance. A discriminant function analysis, which included neuroradiological findings, injury severity, and medical complications, could not accurately predict impaired balance ratings. Conclusions: This study demonstrated that rehabilitation admission balance ratings have a significant relationship with age, multiple measures of severity, and acute care medical complications after TBI. Prospective studies are indicated to evaluate the role balance at rehabilitation admission plays in the functional prognosis of patients with TBI.