All surgically treated cases of hydatidosis registered in Sardinia from 1969 to 1984 have been analysed. The 16-year period clearly shows that unilocular hydatid disease caused by larvae of tapeworm, Echinococcus granulosus, is endemic in Sardinia. In this region there are foci of human infection notably in the sheep rearing areas, of Nuoro and Sassari. The incidence of human hydatidosis shows a marked regional variation varying during the last survey (1982-1984) between 16.9/1000 in the province of Nuoro to 8.3/1000 in the province of Cagliari. Not all population is at equal risk e.g. 47.1/1000 is the incidence in shepherds respect to 8.9/1000 in employed in services. In Sardinia, although there are a wide variety of suitable intermediate host species, is sheep the determinant host for the perpetuation of the parasite's life cycle. The prevalence rate in cattle, pigs and goats in under 30% while the sheep incidence is extraordinarily high, over 90% are infected. The dogs showed a prevalence rate of 10-20%, the infection was more frequent in shepherd-dogs and strays. The rate of hydatidosis in man appears significantly correlated with number of dogs and sheep per inhabitants. Two factors are, at present, determinant in the dissemination of hydatidosis: the common sardinian practice of slaughtering sheep at home and the indiscriminate proliferation of dogs which mainly live as strays. The epidemiological picture and the economic consequences of hydatidosis in man and livestock, a damage of 28 billions of liras per year, strongly suggest this disease as a major public health problem in Sardinia.