Paratuberculosis was brought to Iceland in 1933 by the import of infected sheep from Germany. The infection in sheep spread rapidly throughout the main sheep breeding areas and attempts to eradicate the disease were unsuccessful. These included quarantine areas, widespread immunological testing, extensive culling of sheep in endemic areas and restocking with healthy sheep. Vaccination experiments on the other hand gave good results and showed that mortality could be reduced by 94%. The Icelandic strain of M. avium subsp. partuberculosis is a sheep strain and infects both sheep and cattle. Since 1966 vaccination of sheep has been compulsory in endemic areas and losses from paratuberculosis have been reduced considerably. The vaccine used is a heat killed vaccine produced in Iceland. The country is divided into 36 quarantine areas with boundaries made up of hundreds of kilometres of fences and natural geographic hindering. The quarantine areas are categorized as: 1) areas where paratuberculosis has never been diagnosed, 2) areas with compulsory vaccination, 3) areas where vaccination has been stopped. In 2001 paratuberculosis suddenly appeared on a farm in an area which had been declared free from paratuberculosis. This was a major drawback, as vaccination had been stopped in the whole quarantine area 3 years earlier. Sheep from all farms in the area were then tested serologically, using both ELISA test and Complement Fixation Test. Out of a total of 400 sheep on the affected farm, 50 were seropositive and/or had clinical symptoms. One seropositive sheep was found on another farm. All other farms in the area were seronegative. All positive animals on the two farms were culled and the rest vaccinated. Vaccination is now compulsory again in the whole quarantine area. The reason for the outbreak is still unclear and this raises the question whether eradication of paratuberculosis by vaccination is possible or not.