In 2006, bluetongue virus serotype 8 (BTV-8) caused the first recorded bluetongue outbreak in northern Europe. This occurred in countries with no previous history of bluetongue virus incursion, including the Netherlands, Belgium and Germany. Following a halt to disease transmission over the winter, the virus re-emerged in 2007, spreading throughout northern Europe and eventually reaching the UK in September 2007. The chances that BTV-8 will emerge again in the UK in 2008 are considered to be very high. Due to the wide spectrum of clinical signs and variation in severity of disease seen in cattle and sheep with bluetongue, a variety of diseases may resemble some or all features of bluetongue infection. This article describes the main differential diagnoses of bluetongue in cattle and sheep, and summarises the distinguishing features and laboratory tests that can assist in their differentiation.