Neurotrophic factors are essential contributors to the survival of peripheral and central nervous system (CNS) neurons, and demonstration of their reduced availability in diseased brains indicates that they play a role in various neurological disorders. This paper will concentrate on the role of brain-derived neurotrophic factor (BDNF) in the survival and activity of the neurons that die in Huntington's disease (HD) by reviewing the evidence indicating that it involves profound changes in BDNF levels and that attempts to restore these levels are therapeutically interesting. BDNF is a small dimeric protein that is widely expressed in adult mammalian brain and has been shown to promote the survival of all major neuronal types affected in Alzheimer's disease (AD) and Parkinson's disease (PD). Furthermore, cortical BDNF production is required for the correct activity of the corticostriatal synapse and the survival of the GABA-ergic medium-sized spiny striatal neurons that die in HD. We will highlight the available data concerning changes in BDNF levels in HD cells, mice and human postmortem samples, describe the molecular evidence underlying this alteration, and review the data concerning the impact of the experimental manipulation of BDNF levels on HD progression. Such studies have revealed a major loss of BDNF protein in the striatum of HD patients which may contribute to the clinical manifestations of the disease. They have also opened up a molecular window into the underlying pathogenic mechanism and new therapeutic perspectives by raising the possibility that one of the mechanisms triggering the reduction in BDNF in HD may also affect the activity of many other neuronal proteins.