BACKGROUND Optic neuritis is a rare but possible complication of sphenoid sinusitis. CASE REPORT We present a case of a young woman with recurrent optic neuritis associated with chronic sphenoid sinusitis. A 29-year-old woman with visual impairment of the left eye to Snellen distance best-corrected visual acuity (DBCVA) of 0.5 and migraine headaches accompanied by vomiting and dizziness reported to the ophthalmic emergency room. The preliminary diagnosis was demyelinating optic neuritis. On head computed tomography, a polypoid lesion of the sphenoid sinus was found and qualified for elective endoscopic treatment. During a 4-year follow-up, evaluation of DBCVA, fundus appearance, visual field, ganglion cells layer (GCL), peripapillary retinal nerve fiber layer (RNFL) thickness, and ganglion cells and visual pathway function (pattern electroretinogram - PERG, pattern visual evoked potentials - PVEPs) were performed. Four years after the occurrence of the initial symptoms, surgical drainage of the sphenoid sinus was performed, which revealed a chronic inflammatory infiltrate and a sinus wall defect on the left side around the entrance to the visual canal. After surgery, headaches and other neurological symptoms resolved, but DBCVA deteriorated in the left eye to finger counting/hand motion, partial atrophy of the optic nerve developed, the visual field defect progressed to 20 central degrees, GCL and RNFL atrophy appeared, and deterioration of ganglion cells and visual pathway function were observed. CONCLUSIONS In patients with optic neuritis and atypical headaches, sphenoid sinusitis should be considered in the differential diagnosis. Delayed laryngological intervention can cause irreversible damage to the optic nerve.