The genetic structure of Lugovye Maris was studied on the basis of marital migration. Malecot's parameters of isolation and endogamy index were estimated in four rations of the Marii El Republic, which is populated by Maris. High values of the endogamy index (0.80 and 0.88) never observed previously in any Russian populations, were revealed in two rations. The lack of significant correlation between endogamy and local inbreeding was analyzed. A significant correlation (0.70) between endogamy and effective population size was revealed.