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Purpose To present a case of symptomatic optic nerve sheath calcification and highlight clues and pitfalls for the final diagnosis: bilateral optic nerve sheath meningioma. Observations A 48-year-old man presented with painless vision loss in his left eye and findings consistent with left optic nerve atrophy. Magnetic resonance imaging (MRI) displayed thinning of the left optic nerve without contrast-enhancement or evidence of compressive lesions. A supplementary computed tomography angiography (CTA) exposed scattered dural calcification, which included the optic nerves. This was regarded as an incidental finding. The initial diagnosis was ischemic optic neuropathy. Over the next two years, the vision loss in the left eye progressed. A CT of the orbits revealed extensive calcification surrounding both optic nerves. A second MRI was unchanged in comparison to the first MRI. The diagnosis was changed to idiopathic duro-optic calcification. The vision in the left eye further declined over another two years. Consecutive optical coherence tomography measurements of the peripapillary retinal nerve fiber layer suggested bilateral progressive thinning. A third MRI displayed progression of tubular contrast-enhancement surrounding the optic nerves. On the basis of this finding, the patient was finally diagnosed with a bilateral optic nerve sheath meningioma and received external beam radiotherapy. Conclusion and importance It is crucial to differentiate an optic nerve sheath meningioma from idiopathic calcification of the optic nerve. In the present case the initial MRI did not detect optic nerve sheath abnormalities. To better demonstrate characteristic calcification, additional CT imaging should be considered when a bilateral optic nerve sheath meningioma is suspected.