A 9-year-old Latin American girl developed proptosis of the left eye associated with pain in the left ear of one month's duration. Ophthalmoscopic examination of the left eye disclosed retinal striae with venous tortuosity and papilledema. CT scan of the orbit showed a nonenhancing, irregular intraconal mass. CT scan of the brain demonstrated an enhancing left temporoparietal mass. Craniotomy revealed a 7 cm, extra-axial mass that was attached to the dura mater. Histologic examination, including a positive Leder stain, established the diagnosis of granulocytic sarcoma. At that time, the results of the laboratory studies, including complete cell blood count, were normal. Periodic clinical and hematologic evaluation was recommended. Twenty-five days after craniotomy, examination of the peripheral blood disclosed 56% myeloblasts and the bone marrow contained 30% blast cells. The problem in histologic differential diagnosis and a review of the literature is discussed.