A geographic information system was used in an epidemiological study of measles in Istanbul, Turkey. The aim was to obtain more reliable results and to increase the facilities for spatial monitoring in epidemiological studies. The Gaziosmanpasa district of Istanbul was selected as it experiences the highest level of migration, and currently has the highest population growth rate of the city's districts. The epidemic distribution of measles was investigated on the basis of examination of 320 children. The number, geographical distribution, complications and time of measles outbreaks were analysed and represented in thematic maps (a small selection is shown in this paper). The results were evaluated and, in view of these results, new vaccination plans were arranged.