Relapse is one of the inherent clinical signs of multiple sclerosis (MS), but an assessment of the factors that can affect the aggravation of MS remains inadequate. According to the available studies, there are contradictory results regarding seasonal factors that can affect the frequency of relapses. The purpose of this study — to assess the impact of environmental factors on the frequency of exacerbations of MS in the remitting-recurring course of four consecutive years of observation. Materials and methods. Our study envisaged the complete registration of all cases of exacerbations of MS in the Volyn region, because to date no large-scale studies have been conducted on the change of seasonal recurrence of MS in Ukraine. A prospective study of exacerbations in patients with MS was conducted for further study of seasonal fluctuations in the frequency of relapses and comparison of observed patterns with selected climatic variables. Results. During the four-year interval from January 2014 to January 2018, 197 exacerbations were registered in patients with MS (n=128). The statistical analysis of the data showed the predominance of exacerbations in the winter and spring periods and showed the presence of weak and average correlation between factors (t_av, t_max, t_min, partial pressure of water vapor, relative humidity, saturation deficits, S¹, D, Q, B, Ak, T, wind speed, total cloud, low cloud, fog, light thunderstorm, large thunderstorm, hail) and the frequency of exacerbations of the MS. It has been established that seasonal recurrence of MS should be considered as the result of multifactorial effects, rather than the effects of individual, disparate factors. It is also suggested that the low status of vitamin D is a consequence rather than a risk factor for MS in general and relapse in particular.