Objectives: To present the clinical features, determine the causes and evaluate the prognosis of orbital apex syndrome in patients of Songklanagarind Hospital. Methods: A retrospective review was conducted of patients diagnosed with orbital apex syndrome between January 1, 2002 and December 31, 2008. Results: In our series, the major cause of orbital apex syndrome was carotid-cavernous sinus fistula, for which 30 patients were diagnosed. After excluding those patients whose condition was caused by carotid-cavernous sinus fistula, 50 patients (58 eyes) were analyzed. The mean age of the patients was 47.60 +/- 18.88 years (27 male patients and 23 female patients). The most common presenting symptom was blurred vision (86%). The median duration of the presenting symptom was 37.5 d. Of the 50 patients the most frequent aetiology of orbital apex syndrome was neoplasia (48%), of which lymphoma was the most common in this group. After treatment, the vision of 19.4% of the patients improved and proptosis improved by 68.4%. Conclusions: The most common presenting symptom of orbital apex syndrome was blurred vision. The most frequent aetiology of orbital apex syndrome of all patients was carotid-cavernous sinus fistula, while the next most frequent was neoplasm, of which lymphoma was the most common in this group. Patients had a good outlook, after treatment directed at the cause, with a modest improvement in vision and exophthalmos in more than half of patients.