Balance dysfunction is commonly observed following traumatic brain injury. There are many proposed predictors of functional outcome in the traumatic brain injury population. It was hypothesized that the degree of balance dysfunction on admission to rehabilitation would be a significant predictor of the need for assistance at discharge, as measured by the Functional Independence Measure (FIM). This study involved 237 cases of traumatic brain injury patients admitted to a rehabilitation unit between November 1989 and September 1996. Using a multiple regression model, controlling for age, initial Glasgow Coma Score (GCS), rehabilitation admission strength, sitting balance and standing balance, it was found that the degree of impairment in sitting balance at admission to rehabilitation was a significant predictor of Discharge FIM-Total (FIM-T) score (p < 0.0001) and also of selected elements from the Discharge FIM-Motor (FIM-M) score (p < 0.0005). The combination of age, initial admission GCS, rehabilitation admission strength, standing balance and sitting balance accounted for 29% of the variance in the Discharge Total FIM score. Among these, sitting balance was the second most powerful predictor of both selected elements of the Discharge FIM motor score and discharge FIM-T. Sitting balance predictive capacity was exceeded in power only by age. Impairments in sitting balance appear to have a significant impact on functional outcome. Emphasis on unique rehabilitation techniques to treat balance dysfunction in the adult TBI population is warranted.