Brain derived neurotrophic factor (BDNF) regulates diverse neuronal functions and plasticity, and its expression is increased by seizures. Here we review the evidence that actions of BDNF at TrkB receptors contribute to temporal lobe epilepsy. In addition, regulation of BDNF by steroid hormones might explain syndromes such as catamenial epilepsy. For an expanded treatment of this topic see Jasper's Basic Mechanisms of the Epilepsies, Fourth Edition (Noebels JL, Avoli M, Rogawski MA, Olsen RW, Delgado-Escueta AV, eds) published by Oxford University Press (available on the National Library of Medicine Bookshelf [NCBI] at). © 2010 International League Against Epilepsy.