To determine the diagnoses in a population of patients with presumed optic neuritis (ON) in China and compare the spectrum of etiologies with those in western countries, we studied a group of 204 patients referred to a teaching hospital with a presumptive diagnosis of ON. We conducted detailed medical and family history, thorough ophthalmologic and neurological examinations, and laboratory tests including neuroimaging. Patients were diagnosed using international diagnostic criteria. One hundred and thirteen patients (55.4%) met ON criteria, among whom 83 patients (73.5%) were diagnosed with idiopathic demyelinating optic neuritis (IDON). Brain MRI white matter lesions were found in 11 of 78 (14.1%) clinically "isolated" IDON patients. Tuberculosis meningitis was found in 2 patients and syphilis in 1 patient. The cause of ON in 26 patients (23.0%) remained uncertain, but it was still likely to be IDON accompanied by secondary axonal degeneration. Leber's hereditary optic neuropathy (LHON) was found in 38 patients (18.6%), confirmed by mitochondrial DNA point mutation screening. Seventeen patients (8.3%) had ischemic optic neuropathy. A spectrum of other entities mimicked ON. Therefore, idiopathic demyelinating ON was the most common type of optic neuropathy in our group. Despite minor differences regarding the causes and prognosis, the etiology of ON in our population is similar to that reported in Western countries. (C) 2008 Elsevier Ltd. All rights reserved.