Fever frequently presents during recovery from traumatic brain injury (TBI). Elevated body temperature may result from ensuing infection, thrombophlebitis, drug reaction, or a defect in the central thermoregulatory system such as seen in post-traumatic hyperthermia (PTH). Typically, the diagnosis of PTH follows only after thorough investigation. Literature supports the theory that the febrile TBI patient, lacking a documented source, has central hyperthermia. The purpose of this study was to determine the incidence of PTH in the acute rehabilitation setting. We reviewed a consecutive series of 84 TBI patients participating in a rehabilitation programme. Four per cent of the patients in this study met our criteria for PTH. We describe a fever protocol that should aid the physician in diagnosis and treatment of the febrile TBI patient. Proposed mechanisms involved in thermoregulation are discussed.