Brain-derived neurotrophic factor (BDNF) expression in rat hippocampus is increased after experimental traumatic brain injury (TBI) and may be neuroprotective. Glucocorticoids are important regulators of brain neurotrophin levels and are often prescribed following TBI. The effect of adrenalectomy (ADX) on the expression of BDNF mRNA in the hippocampus after TBI has not been investigated to date. We used fluid percussion injury (FPI) and in situ hybridization to evaluate the expression of BDNF mRNA in the hippocampus 4 h after TBI in adrenal-intact or adrenalectomized rats (with or without corticosterone replacement). FPI and ADX independently increased expression of BDNF mRNA. In animals undergoing FPI, prior ADX caused further elevation of BDNF mRNA and this upregulation was prevented by corticosterone replacement in ADX rats. These findings suggest that glucocorticoids are involved in the modulation of the BDNF mRNA response to TBI.