Newcastle disease (ND) is a highly contagious and often severe disease found worldwide that affects birds including domestic poultry. It is caused by virulent strains of avian paramyxovirus type 1. The disease appears in three forms: lentogenic or mild, mesogenic or moderate and velogenic or very virulent, also called Newcastle disease. The lentogenic strains are very widespread but cause few disease outbreaks. It usually presents as a respiratory disease, but depression, nervous manifestations, or diarrhoea may be the predominant clinical form. Newcastle disease, in its highly pathogenic form, is a WOAH listed disease and must be reported. ND can present a clinical picture very similar to avian influenza, so laboratory testing is important to confirm the diagnosis.