OBJECTIVE The purpose of this study was to investigate the scolicidal effect of intracystic injection of benzimidazolic solutions in naturally infected sheep with hydatid disease. METHODS Twenty-four sheep with 37 hydatid cysts were included in this study for percutaneous treatment with benzimidazolic solutions. The animals were divided into 3 groups: group I, treatment group with mebendazole; group II, treatment group with albendazole; and group III, control group with distilled water. All solutions were given percutaneously under sonographic guidance. Cyst contents were aspirated with a needle, and then scolicidal solutions were injected into the cysts; reaspiration was not done. Routine follow-up sonographic images were taken on the 15th day after treatment, then once per month for 3 months, and then at 3-month intervals thereafter. At the 1-month follow-up, the percutaneous aspirate yielded orange juice-like material containing necrotic debris without living scolices. RESULTS Sonography showed a reduction in cyst size in the benzimidazolic groups (groups I and II) and progressive changes in echo patterns. An anaphylactic reaction was observed during the procedure in 1 animal. After 12 months of sonographic follow-up, the animals in all groups were killed, and macroscopic and microscopic changes in tissue samples were evaluated. At autopsy, no cysts with living scolices were found in the benzimidazolic groups, and the appearance of the treated cysts was different from that of those in the control group. Microscopic examination showed the degeneration, necrosis, and thickening of the cyst walls in the treatment groups. CONCLUSIONS Intracystic injection of benzimidazolic solutions as scolicidal agents may be used for percutaneous treatment of hepatic hydatid cysts in sheep.