The case of a 30-year-old woman who had two episodes of photopsia along with sudden-onset monocular visual field defects, developing into bilateral tunnel vision within 4 years, is reported. She also had episodes of a right hemiparesis and right-sided hypoaesthesia, accompanied by severe fatigue. This patient fulfilled the criteria for both clinically definite multiple sclerosis and acute zonal occult outer retinopathy (AZOOR). AZOOR can have an onset with monocular visual field loss, and can be distinguished from optic neuritis. In addition, some observations suggest common neuropathological and inflammatory mechanisms between multiple sclerosis and AZOOR.