Thin-needle aspiration biopsy (TNAB) was performed on 22 patients with orbital tumors. Nine patients were studied before the introduction of computed tomography (CT) and only two cytologic diagnoses could be established. Thirteen aspiration biopsies guided by CT were successful. The technique of the CT-guided TNAB of orbital tumors is described. The cytologic features combined with the clinical data made it possible to diagnose precisely 10 malignant orbital tumors that were either metastatic or primary. Two meningiomas and one abscess were also identified. There were no complications. The TNAB of orbital tumors under CT guidance appears to offer several significant benefits to the patients.