The authors reviewed 35 cases of orbital hydatid cysts, which represented 5% of orbital surgical cases seen from 1944 to 1985. The average age was 16 years (range, 2-57 years). Slowly progressive unilateral exophthalmos, with or without pain, was the most frequent clinical manifestation. Computed tomography (CT) of the orbit demonstrated a well-circumscribed mass. Ultrasonography showed an anechoic cystic mass. The parasitic membrane and contents were surgically removed through an orbital approach. Hydatid cysts should be included in the differential diagnosis of unilateral exophthalmos in patients from countries where echinococcosis is endemic. Preoperative recognition is important for planning an appropriate surgical treatment in avoiding complications.