The purpose of the present study was to look at possible gender differences in outcome after severe traumatic brain injury. Three hundred and thirty four consecutive patients, 72 females and 262 males, age range 5-65 years, were included in the study. Age range and severity of injury, evaluated by duration of unconsciousness, did not differ between male and female patients. Predicted outcome at the time of discharge from an in-patient rehabilitation programme was evaluated according to work capacity. Female TBI patients had a better predicted outcome (p < 0.015). It is suggested that progesterone, acting as a neuroprotective agent, may explain this difference in outcome.