Prevalence of multiple sclerosis (MS) was evaluated in the pilot study of 731 patients living in Tyumen city and a southern part of Tyumen region as well as in Khanty-Mansi (KMAO) and Yamal-Nenets (YNAO) autonomic okrugs. An index of MS prevalence was 22,4 per 100,000 in Tyumen region as a whole. This index was higher--29.1 per 100 000 - in the southern part. In KMAO and YNAO, the MS prevalence was 14,3 and 27,8 respectively. Women prevailed among patients in all the regions, their number being twice higher (461 and 270). However, if in the southern part and in KMAO this ratio was approximately equal, in YNAO percentage of men was significantly higher. It should be noted that these data need further study. We revealed that using of current diagnostic criteria may often lead to misunderstanding of diagnosis of "definite" MS. Essential difference in MS prevalence in different regions may be explained by ethnical stratification. In particular, there are many newly migrated people in the okrugs and MS occurs more often in that group. At the same time, there is no any information on the prevalence of "definite" MS among the native-born population of KMAO and YNAO.