Optic neuritis (ON) refers to any inflammatory optic neuropathy. In clinical practice ON is mainly diagnosed by ophthalmologists and less frequently by neurologists. ON diagnostic criteria are included in the Classification of International Headache Society (IHS) and in other classification systems, both in neurological and ophthalmologic fields. The aims of this study were to verify the application of IHS ON diagnostic criteria in clinical practice and the role of the ocular pain qualitative aspects. We performed a partially retrospective (140 cases) and prospective (43 cases) study analysing the clinical characteristics of patients with ON. We observed retro orbital pain in a huge percentage of patients; it was provoked or spontaneous and worsened by eye movements. We found that the new IHS classification criteria (IHS 2004) do not fully satisfy the requirements for ON diagnosis. Further study is necessary to validate the diagnostic criteria of ON in clinical practice.