To determine the cost of health care services received by persons hospitalized with traumatic brain Injuries, a population-based sample of Individuals treated at the trauma centers in El Paso County, Colorado, was followed retrospectively for 4 years after injury. Of the random sample of 251 survivors who sustained brain trauma in 1989 and 1990 (stratified by severity), 127 were successfully located and agreed to participate in the research. All medical services provided were identified through both medical record review and extensive patient interviews. Actual charges were obtained directly from the 482 vendors serving these clients. Mean charges for initial hospitalization (including acute care and rehabilitation) ranged from $17,015 for mild injuries to $133,467 for severe injuries. Four-year follow-up charges for rehospitalizations, physician visits, outpatient services, medications, equipment and supplies, attendant care, and miscellaneous services ranged from a mean of $2,323 for mild Injuries to $54,701 for severe injuries. At an incidence rate of 69 per 100,000, it is projected that the total costs for new cases of hospitalized traumatic brain Injury in any given year in the United States will exceed $8 billion over the course of the first 4 years following injury.