PURPOSE: To describe the percutaneous treatment of an orbital hydatid cyst as an alternative approach to conventional surgery. METHODS: In a 21-year old man with diplopia and right proptosis, radiologic studies disclosed a 25 x 25 x 20-mm purely cystic mass in the right retrobulbar area. Based on the presumptive diagnosis of hydatid cyst, the cyst was treated percutaneously under ultrasonographic guidance with aspiration, 15% hypertonic saline injection, and reaspiration without any complication. RESULTS: A substantial decrease in the size of the cyst was observed in the 3 months after treatment. Nine months after treatment, the shrunken cyst had a volume of only 0.5 ml, and the patient was asymptomatic. Twenty-one months after the procedure, the findings were consistent with those at 9 months of follow-up. CONCLUSION: Percutaneous treatment of orbital hydatid cysts, which is more satisfactory to both the patient and the physician, may be a safe and effective alternative to surgical extirpation. (C) 1998 by Elsevier Science Inc. All rights reserved.).