Seven naturally infected sheep with proper hepatic and peritoneal hydatid cysts were studied to assess a new percutaneous approach for cystic hydatid disease. A needle was inserted into the cyst cavity of sheep under sonographic guidance. Immediately after instillation of hypertonic saline to inactivate protoscolices, ultrasound demonstrated that germinal and laminated membranes of the hydatid cysts were separated completely from the pericyst in all sheep. Later, a catheter was inserted into the cyst cavity using Seldinger technique. Alcohol was used as a sclerosing agent. Ultrasound showed reduction in cyst size and progressive solidification. No anaphylactic reaction was observed. After sonographic follow-up that lasted from 1 to 26 weeks, the sheep were killed to evaluate macroscopic and histologic changes. At autopsy, no secondary cyst formation was seen. The appearance of treated cysts was different from the others, and there were signs of involution. The histologic sections did not show any viable protoscolices or daughter cysts. The authors observed pericyst hyalinization, inflammatory cells in the cyst wall, cyst wall necrosis, calcification of cyst wall, degeneration of laminated membrane, severe degeneration or absence of germinal membrane, and inflammatory cells and necrotic material in the cyst cavity. Percutaneous treatment of hydatid disease was effective in the animal model. Ultrasound was useful in evaluating the intervention.