A 4-year-old healthy girl with acute visual loss in the right eye had ophthalmoscopic evidence of a swollen optic disc combined with central retinal artery and vein occlusion in the affected eye. MRI showed that the intraorbital optic nerve on the affected side was thickened and enhancing. Diffusion-weighted imaging showed restricted diffusion in the distal intraorbital segment of the optic nerve, consistent with infarction attributed to compression or inflammation of the vessels serving the optic nerve and retina. Although such clinical phenomena have been described previously, this is the first patient to demonstrate restricted diffusion in an inflammatory optic neuropathy. The presence of restricted diffusion is helpful in excluding a neoplastic cause of a thickened optic nerve.