Seroepidemiological study of human hydatidosis in San Juan de la Costa County, Osorno, X Region, Chile, 2000. San Juan de la Costa County (40º 45' South lat., 73º 19' West long.) is located in the Osorno province, South of Chile. Its population is 11,445. The basic economic activities are agriculture,cattle raising, fishery, timber production and manufacture of wood and coal. According to official reports, the incidence of human hydatidosis in Chile and Osorno province, in 1999, was 1.8 and 12.5 per 100,000 respectively. In order to contribute to a better knowledge of the epidemiology of human hydatidosis, an indirect hemagglutination test (IHAT) and ELISA IgG for hydatidosis were performed to 533 randomized people. Three (0.56%) resulted positive. Parallelly, a socio-epidemiological survey on hydatidosis was carried out: the majority of people had some basic knowledge about some aspects of hydatidosis transmission. Some considerations on the corresponding prophylatic measures are mentioned.