A five-and-a-half-year-old boy with neurofibromatosis had bilateral orbital optic gliomas visible on magnetic resonance imaging. Both tumors displayed a double-intensity signal characterized by a circumferential area of CSF-intensity tissue surrounding and sharply delimited from a central linear core of opposite signal intensity. The peripheral CSF-intensity signal in orbital optic glioma correlates with the histopathological finding of perineural arachnoidal gliomatosis and serves as a neuroradiologic marker for neurofibromatosis.