The prevalence of factors associated with functional disability was estimated six and twelve months after traumatic brain injury (TBI) in patients initially treated in the emergency unit of reference for the Metropolitan Region of Salvador, Bahia, Brazil. A prospective cohort study was performed, including 307 individuals with TBI between the ages of 15 and 65 years whose diagnosis was confirmed via neuroimaging. Using data from the period of hospitalization, 242 patients were contacted six months after the injury and 222 patients after twelve months. Functional impairment was evaluated with the Disability Rating Scale. The overall prevalence of functional disability (60.3% in the first evaluation and 40.5% in the second) was significantly associated with age, the initial gravity of the TBI and the duration of the patient's hospitalization, as well as with: fatigue; aphasia; memory, attention and concentration disorders; balance disorders; paresis; and lack of medical consultations with specialists. The high frequency of overall functional disability in the six or twelve-month follow-up period, even for patients with mild traumas, shows the relevance of TBI as a cause of disability and impairment, as well as the need for follow-up services.