To investigate the etiology and prevalence of optic neuritis in a Chinese population. This was a single centre prospective cohort study. Consecutive patients with either a first or recurrent attack of optic neuritis from November 2010 to December 2011 were recruited from a district hospital in Hong Kong Special Administrative Region, China. All patients underwent serology testing for NMO (neuromyelitis optica) IgG; oligoclonal bands from lumbar puncture; computer tomography and contrast magnetic resonance imaging (MRI) of the brain and orbit as well as visual field; and optical coherence tomography testing. Patients were followed up for 1 year after the initial attack. 30 optic neuritis subjects were recruited. 73.3 % (22/30) remain as clinical isolated syndrome (CIS) after 1-year follow-up. 10 % (3/30) patients developed multiple sclerosis. 10 % (3/30) were diagnosed with NMO and 6.7 % (2/30) with NMO-spectrum disorder. The majority of acute unilateral optic neuritis in Chinese was CIS in origin although a fraction does progress to develop MS or NMO-related disorders. Clinicians should be aware of the associations and offer appropriate systemic workups.