Eight cases of primary optic nerve sheath meningioma were treated between 1980 and 1988. Five were females aged 37-61 years. The other three were two boys, one with neurofibromatosis, and an old male aged 71 years. They were first seen by the ophthalmologist with complaints of unilateral progressive visual loss or proptosis. Although blindness of the affected eye mainly occurred between 1 month and 3 years after the initial symptoms, the diagnosis tended to be made late in the adult cases. Intracranial extension was demonstrated in four of the six adult cases when contralateral visual loss or disturbance of consciousness presented. Larger intraorbital meningiomas were easily diagnosed by a combination of computed tomographic (CT) scanning, magnetic resonance (MR) imaging, and carotid angiography. MR imaging provided clear delineation of the optic nerve and its course through the tumor, and perioptic meningioma could be diagnosed. However, it was difficult to make a diagnosis without biopsy at the early stage, for example, when just the enlargement of the optic nerve was demonstrated by CT or MR imaging. Tumor removal was performed when blindness developed after definitive diagnosis by biopsy, intracranial extension was demonstrated, and advanced proptosis presented. The transcranial supraorbital approach or transcranial transorbital approach with resection of the supraorbital rim was used for these large intraorbital meningiomas. From our clinical experience, early diagnosis and early treatment should be emphasized.