The occurrence of Echinococcus multilocularis in the Poland-Slovak frontier zone of the East Carpathian region was assessed, for comparison with that in adjacent regions in both countries. A total of 392 red foxes from Poland and 427 red foxes from the Slovak Republic were examined from 2001 to 2004. Significant differences in prevalences were observed in foxes captured from the borderland and adjacent zones in both countries. The mean prevalence of E. multilocularis in the Polish borderland reached 45.7+/-18.6% and in the Slovak border 35.0+/-10.7%. In both countries, the prevalence of E. multilocularis in red foxes from adjacent districts, outside the frontier Carpathian region, was considerably lower (18.9+/-9.2% in Poland and 20.8+/-9.0% in Slovakia). These differences are probably due to geomorphological and ecological factors, which contribute to the survival of the tapeworm eggs and the subsequent spread of infection. The Carpathian regions of northeast Slovakia and southeast Poland are characterized by specific climatic conditions such as low mean annual air temperatures, low temperatures in active soil surfaces, high soil humidities and a high mean annual rainfall.