West Nile Virus (WNV), is an arthropod-bome flavivirus that can cause a variety of neurological symptoms in humans, horses, birds and wild animals. The virus causes mild febrile illness, meningitis, encephalitis or death in humans and many animals such as, dogs, horses, birds in America, Asia, Africa, Europe and particularly in countries bordering the Meditterranean Sea. In this article; the etiology, pathogenesis, symptoms of and diagnostic methods for WNV are reviewed.