Optic nerve sheath meningiomas and optic nerve gliomas can be difficult to differentiate by computed tomography (CT). Three patients with optic nerve sheath meningiomas were studied with a CT/T 8800 scanner with 1.5-mm-thick axial sections and intravenous contrast material. In each case, an abnormal optic nerve sheath was identified by CT. A soft-tissue mass arose from one side of the sheath in one patient, and the entire sheath was enlarged in two patients. This provides a basis for distinguishing optic nerve sheath meningioma from optic nerve glioma.