Background/Aim. Multiple sclerosis (MS) is an immunemediated disorder of the central nervous system (CNS), characterized by inflammation, demyelination and axonal loss. Retinal periphlebitis (RP) is often present in MS patients with similar evolution and histopathological changes as MS lesions. The aim of this study was to analyze the presence of RP in MS patients during different clinical phases, and its connection with impairment of blood-brain barrier. Methods. The study included 45 patients (26 females and 19 males) with MS. Their average age was 33.2 ± 8.1 years. There were 28 patients with relapsing-remitting (RR) form, 7 with primary progresive (PP) and 10 with secondary progressive (SP) form of MS. There were 27 patients in the relapse and 18 patients in the remission phase. The average MS duration was 7.48 ± 1.3 years. Ophthalmological, neurological and MRI examination were performed in all the patients, as well as cerebrospinal fluid sampling. Albumin ratio and IgG index were calculated in all the patients. Results. There were 9 patients with RP, and 36 without it. MS duration was significantly longer in the RP group. RP was much more common in the progressive form and was not present in the remission phase of MS. Albumin ratio values were increased in the group with RP. IgG index and IgG synthesis according to Tourtellotte formula, were statistically higher in the group of patients with RP. The values of visual evoked potentials (VEP's) latency were significantly higher in the group of patients with RP. Conclusion. The presence of RP is a reliable indicator of MS activity and might be considered as a parameter for monitoring the disease activity and effects of the treatment.