Japanese encephalitis (JE) vaccine has been used in childhood immunization programmes in Asia for many years. Also travellers from other parts of the world have been vaccinated before travelling in Asian countries. Recommendations for the use of JE vaccine are still debated because severe cases of adverse reactions have been reported. In Denmark an inactivated JE vaccine derived from infected mouse brain has been used and 350000 doses have been distributed from the Statens Serum Institut since 1983. In the period 1983-1995, 101 adverse reactions after JE vaccination have been registered including 73 allergic mucocutaneous reactions. These reactions have occurred each year since 1989 with frequencies varying from 1-17 per 10,000 vaccinees. The highest frequencies and the most serious reactions acquiring hospitalization were seen in the period 1989-1992. Three batches (EJN 012, 033 and 048) distributed before 1992 caused the highest number of reactions but all batches delivered in Denmark since 1989 have caused reactions. Therefore, it is still very important to collect information on adverse events as well as information of the risk of acquiring JE infection in order to give sound recommendations to travellers.