The clinical syndrome of acute optic neuritis(ON) has been known for many yearsthough its causes are still uncertain. Especially, the main focus is how often after a firstbout of isolated ON progress to multiple sclerosis in neurologic field. Therefore westudied and analysed 20 patients with acute optic neuritis for clinical features and prognosis and obtained the results as follows; 1. The male to female ratio was 1: 4. 2. The age at onset ranged from 9 to 70 years. 3. Unilateral involvement -of ON was detected in 10 cases (50%); the others were bilater al(10 cases, 50%). 4. Papillitis was present in 6 cases(30.2%) and the disk was normal(retrobulbar) in the other 7 cases (35%). 5. Recovery of vision was noted within 2 weeks in 8 eyes(34.8%) and in 19 eyes (82.2%) within 2 months. 6. The response to treatment in optic neuritis showed no definite difference between steroid group and conservative group. 7. The rate of ON evolving into multiple sclerosis was 10% in this series.