A 45-year-old patient was admitted with high fever and inadequate behaviour. She had recently stayed in Israel. Extensive investigation suggested a viral infection, but the cause was not established. Her partner suggested the possibility of West Nile virus infection, based upon information he had found on the Internet. Serology was performed and specific IgM and IgG antibodies were demonstrated, but a paired serum sample was not available. The patient recovered spontaneously. The West Nile virus is endemic in Israel, Africa, Asia and the Balkans. It is transmitted by mosquitoes. The incubation time is 1-3 weeks. The disease is characterised by fever, malaise, maculopapular exanthema and lymphadenopathy. Complications are encephalitis, pancreatitis, hepatitis and myocarditis. However, these symptoms are present in less than 5% of all infections. A full-blown encephalitis has a mortality rate of 50%. There is no specific therapy, but prevention by means of controlling the mosquito population is feasible. The diagnosis is made by the detection of West Nile virus-specific IgM antibodies in serum or cerebrospinal fluid. However, in the acute stage viral RNA detection by a polymerase chain reaction in the serum is also possible.