A clinical case of optic neuritis in a patient with idiopathic thrombocytopenic purpura is presented. As a result of a comprehensive ophthalmological, clinical, instrumental and laboratory examination, objective signs of unilateral demyelinating damage of the optic nerve were revealed (according to the results of electrophysiological examinations and optical coherence tomography). A year later the patient developed a clinical symptoms of multiple sclerosis, confirmed by magnetic resonance imaging. Associations of multiple sclerosis with other autoimmune diseases are not uncommon, however, only a few cases of multiple sclerosis on the idiopathic thrombocytopenic purpura have been described in the literature. Considering that ophthalmologists in clinical practice may encounter concomitant eye diseases on the diagnosed or debuting autoimmune diseases, it is necessary to conduct an ophthalmological examination with immediate consultation of related specialists.