PURPOSE: To present evidence for a causal relation between optic neuritis and influenza vaccination. METHODS: Case report. In a 59-year-old woman with bilateral optic neuritis, neuro-ophthalmologic examination, magnetic resonance imaging, fluorescent treponemal antibody absorption test, antinuclear antibodies, and complete blood cell count and chemistry were performed. RESULTS: Our patient developed bilateral optic neuritis on two occasions, 1 year apart. No evidence of neuroretinitis, syphilis, or systemic lupus erythematosus was identified. Influenza vaccination was given 2 weeks before the onset of each episode. CONCLUSION: This case provides compelling clinical evidence that implicates influenza vaccination as a cause of optic neuritis.