The main demographic parameters of the population of South Altaians from the Mendur-Sokkon village, Ust'-Kanskii raion, Altai Republic, were studied. This population was classified as a growing one because the population's reproductive size was large (37%), the prereproductive part constituted the majority of the population (52%), and the average number of surviving children per spouse was 2.6. The population studied began to mix with other ethnic groups (mostly Russians and Kazakhs) only recently; therefore, the proportion of interethnic hybrids was only 5%. The tribal structure of the Mendur-Sokkon population was typical of all South Altaians and characterized by stringent observance of exogamous regulations. An ethnically pure core was preserved in the population. The degree of endogamy was 0.36; however, the population mostly exchanged marriage migrants within the Ust'-Kanskii raion. A study of postreproductive females revealed that the average number of surviving children and pregnancies per female was 4.9 and 5.3, respectively; these values were lower than those in indigenous northern Siberian populations studied earlier. The high value of the Crow's index of total selection (Itot = 0.63) was mainly accounted for by the differential fecundity component, I(f) = 0.40, whereas the prereproductive mortality component (Im = 0.16) was considerably lower than in northern Siberian populations (Nganasans, Forest and Tundra Nentsi, Evens, Asian Eskimos, etc.) and closer to the values characteristic of urban human populations.