Abstract In July 2008, the European Commission officially designated the French Agency for food, environmental and occupational health safety (ANSES) as the European Union Reference Laboratory (EU-RL) for equine diseases (apart from African horse sickness). West Nile disease, exotic Equine Encephalitis, Vesicular stomatitis, glanders and melioidosis are studied at ANSES Laboratory for animal health located in Maisons-Alfort (near Paris), while the Laboratory for equine diseases located in Normandy is dedicated to Contagious Equine Metritis, Dourine, Equine Viral Arteritis, Equine Herpes viruses and Equine Infectious Anaemia. The EU-RL on equine diseases aims at providing technical and scientific support to the European National Reference Laboratories and the European Commission, as well as improving, harmonizing and developing new diagnostic tools for the diagnosis of equine diseases (through workshops, trainings, proficiency tests). A proficiency test (PT) on West Nile (WN) serological and molecular diagnosis was organized in 2010, in order to assess the performances of different WN diagnosis tools and to improve the results homogeneity among European countries. 22 and 25 laboratories participated to the serology and RT-PCR proficiency test, respectively. This PT indicated that IgG or competition ELISA tests were well established, on the contrary to IgM ELISA and virus neutralization tests. Moreover, there is a need to develop more specific IgG ELISA. WN real-time RT-PCR diagnosis is functional and efficient in most EC countries, however some participants (8) failed to detect lineage 1b and 2 strains. The detection capacity of lineage 1b and 2 strains needs to be improved, in particular in Europe where a pathogenic lineage 2 virus has been identified since 2004. In conclusion, this European PT highlighted the need for improved, adapted and harmonized diagnosis on WN in Europe.