A total number of 3511 serum samples were collected from chicken farms in Saudi Arabia during summer of 2004 and was tested for the presence of antibodies against type A specific antigen of avian influenza virus using commercial enzyme linked immunosorbent assay (ELISA) kits. Total positive samples represented 45.81%. Broiler positive samples represented 12.73%. While in layers, positive samples were 30.19%. Tissue samples were also taken from 5 chicken farms suffering from high mortality and respiratory signs and the H9N2 and Newcastle disease viruses were isolated and identified from these samples. These results indicate that the mild pathogenic avian influenza subtype H9N2 virus is widespread in poultry flocks in Saudi Arabia and is circulating undetected in most cases. Infection with H9N2 may pass unnoticed unless exacerbated by other co-infections like Mycoplasma gallisepticum or infectious bronchitis virus. Presence of H9N2 virus requires continuous monitoring and surveillance for possible occurrence of mutations and the risk of avian-to-human transmission.