The allele and genotype frequencies of the tetranucleotide tandem repeat (TTR) of CFTR intron 6B were analyzed in eight ethnic populations of the Volga-Ural region, including Bashkir, Tatar, Chuvash, Mari, Mordvinian, Udmurt, Komi-Permyak, and Russian. The most common TTR allele 7 varied in frequency from 0.636 in Chuvash to 0.805 in Mordvinians. The frequency of the second common allele 7 ranged from 0.188 in Mordvinians to 0.333 in Chuvash. Allele 8 was found in about 8% of Udmurts and Mari; occurred in a few Bashkirs, Tatars, Mordvinians, and Komi-Permyaks; and was not observed in Russians. The genetic diversity coefficient was minimal in Mordvinians (0.496) and in Tatars (0.505), indicating their low heterogeneity in TTR. The observed heterozygosity was maximal in Udmurts (0.532) and Komi-Permyaks (0.560) and minimal in Mordvinians (0.297). In total, the populations proved to be heterogeneous in TTR allele frequency distribution, the interpopulation difference being significant in most cases.