CRION is a rare cause of optic neuritis. It is usually bilateral, painful and associated with profound visual loss. Significant response to corticosteroid treatment is typical but relapse is common when treatment is withdrawn. We present 2 cases of possible CRION and discuss the diagnostic and management considerations.Case 1: 50-year-old woman presented with right optic neuritis which spontaneous recovered. A year later she had left painful visual loss which improved with a short course of corticosteroids. MRI neuroaxis revealed left optic nerve enhancement. Non-specific, faint unmatched OCBs were detected. AQP4-IgG was negative. Nine months later she had further visual loss in her left eye. Prednisolone and azathioprine were commenced.Case 2: 55-year-old woman with bilateral, painless visual acuity deterioration over two weeks. Investigations revealed negative anti-aquaporin 4 antibodies (AQP4-IgG), normal MRI of the neuroaxis, negative oligoclonal bands (OCBs) and visual evoked potentials showed bilateral delay. Serum ACE was slightly elevated. She was started on a tapering course of steroids and had significant visual acuity improvement.The diagnosis of CRION involves the exclusion of other causes of optic neuritis, particularly multiple sclerosis (MS), Neuromyelitis Optica (NMO) and sarcoidosis. Correct diagnosis is important as aggressive and long-term immunosuppression is required.