The Borna disease virus (BDV) causes a disease of the central nervous system (CNS) in several vertebrate species. The progress made over the last 30 years in molecular biology has allowed us to identify the unique characteristics of the virus, such as its persistence in the CNS and the way it is expressed. This has allowed scientists to classify this pathogenic agent in a new family of RNA viruses. BDV affects a very large spectrum of hosts and is responsible for a disease characterised by behavioural anomalies. The large range of intra- or inter-specific symptoms of this disease (from persistence of the virus without clinical symptoms to CNS destruction) make epidemiological studies very difficult. Different diagnostic tools have allowed the detection of this infectious agent in different species around the world (central Europe, USA, UK, Japan, Iran, etc.). The disease can be fatal for sheep and horses (its primary natural hosts) and can infect other species such as rats, cattle, dogs, cats or pigeons. In human beings, BDV could be responsible for certain psychiatric disorders. In France, the limited number of epidemiological studies that have been conducted up until now (in veterinary and medical fields) does not allow scientists to ascertain whether the disease is present in France or not. Due to the suspected large geographical distribution of this infectious agent, however, we could expect the presence of BDV in France.