Objective: To evaluate optical coherence tomography-angiography (OCT-A) findings and choroidal vascular index (CVI) in patients with multiple sclerosis (MS). Methods: 113 patients, including multiple sclerosis patients with optic neuritis attack (MSON+) and no optic neuritis attack (MSON−) and healthy control group (HCG), participated in this cross-sectional study. OCT-A images of all patients were taken and CVI was calculated. Results: Superior flow (SF), deep flow (DF), foveal, and parafoveal superior vascular density (sVD) were decreased in the MSON+ group compared to HCG (p < 0.05). Optic disk flow (ODF) and optic disk head density (ONHD) values decreased in the MS group (p < 0.05). CVI was decreased in the MSON+ group compared to HCG (p < 0.05). There is a correlation between CVI and foveal and parafoveal sVD. Conclusion: Non-invasive diagnostic tools such as OCT-A and CVI can be used for early diagnosis and follow-up of microvascular pathologies in inflammatory diseases such as MS.