Nine patients--seven women and two men--had meningiomas of the optic nerve sheath. The defect was bilateral in two, in the right eye in six, and in the left eye in one. Most had edema of the disk, and all had progressive loww of vision in the affected eye owing to optic nerve atrophy. In 10 of the 11 affected eyes, opticocilliary shunt veins developed on the optic disk. Exophthalmos was mild and did not measure more than 3 mm in any patient. Ocular movement was mildly impaired in three patients. Indentation and flattening of the posterior pole of the eye were documented in five eyes. Nine of the 11 eyes progressed to blindness; 1 was worse after operation, and the outcome of the 11th is unknown because the patient was lost to follow-up. Surgical treatment has not been effective in these cases or in those reported in the literature.