A history of nervous disturbances and moralities (25%) among young chickens 10-21 day of age as well as a temporary drop in egg production and hatchability (10%) in parent flock occurred in a large poultry farm at EI-Qassiem area, kingdom of Saudi Arabia. Detection, isolation and identifi- cation of avian encephalomyelitis (AE) virus was done using embryonated chicken eggs, immuno- flourscence (IF) and Immunodiffusion (ID) tests. Serological investi gations were carried out on infected sera from both parent flocks and broiler chicks using Enzyme-linked immunosorbant assay (ELISA). Histopathological studies were carried out on samples from naturally infected chick brains as well as brains from inoculated hatched chicks.