Traumatic brain injuries (TBI) impose a significant burden on the health care system. The aim of the current study was to explore variation in costs in a group of rehabilitation patients in Victoria, Australia, following complicated mild-to-severe TBI treated under the accident compensation system administered by the Transport Accident Commission. Study participants included 1237 individuals with mild-to-severe TBI recruited consecutively from a TBI rehabilitation program. Long-term care, hospital, medical, and paramedical costs were obtained 10 years post-injury and their association with demographic and injury-related variables were examined. Significant variability in costs was evident. Long-term care costs were highest, followed by hospital, paramedical, and medical costs. Duration of post-traumatic amnesia (PTA) was a strong predictor of all costs, and stronger than Glasgow Coma Score (GCS). Longer acute hospital stay was related to higher costs. In addition to PTA duration and GCS, other factors associated with higher long-term costs were having an abnormal CT scan and epilepsy early after injury. Higher hospital and medical costs were associated with these factors, but also with other physical injuries, lower education, pre-injury unemployment, living outside the city, speaking English at home, and, in the case of medical costs, older age and having had pre-injury psychiatric treatment. Higher paramedical costs were associated with most of these variables, but also with being employed prior to injury and being female. In line with the multifaceted nature of TBI, the current findings suggest that both injury-related and demographic factors determine costs following injury.