A retrospective study was undertaken to estimate the incidence of hydatidosis among Greeks over 18 years of age. Discharge and operating room records in all community and private hospitals during the period 1 January 1969 to 31 December 1975 were reviewed, and new hydatid patients were registered. Hydatid disease was diagnosed in 4,202 adults. The average annual incidence of all hospital cases was 9.77 per 100,000 population. The diagnosis was confirmed at surgery in 3,397 patients (80.84%). The average annual surgical incidence was 7.89 per 100,000 inhabitants. The incidence of the disease varied among different geographic areas in the country; its percentage was highest in rural areas. In this series, both sexes were equally involved (P greater than 0.1). Solitary organ involvement occurred in 95.88% of cases. Cysts were localized in the liver in 69.64% and in the lungs of 23.43% of the cases with single organ involvement. Liver involvement was more frequent in women, while lung involvement was more frequent in men (P less than 0.001).