Borna disease virus is a nonsegmented negative-strand RNA virus that causes neurologic disease in a wide variety of animal hosts. Here we describe identification and characterization of the first glycoprotein in this viral system. The 18-kDa glycoprotein, gp18, has been purified from infected rat brain. Isolation and microsequencing of this protein allowed identification of a 16.2-kDa open reading frame in the viral antigenome. Lectin binding and endoglycosidase sensitivity assays indicate that gp18 is an unusual N-linked glycoprotein.