• Aim: To investigate the etiology and differential diagnosis of orbital apex syndrome through studying the causes and clinical features. • Methods: Clinical features and the causes of 83 cases of orbital apex syndrome hospitalized from July 1996 to July 2006 and literatures were reviewed retrospectively. • Results: Among 83 patients (89 eyes) of orbital apex syndrome, the most common cause was neoplasm (29,35%), the second was trauma (21,25%), the third was inflammatory (16,19%) and the others were infectious (10,12%), iatrogenic (4,5%), vascular conditions (3,4%). • Conclusion: Orbital apex syndrome can be caused by different diseases. Discussing the differential diagnosis can help to improve the diagnosis rate.