Twenty three groups of thermomineral springs in eastern Chukotka with the discharge temperature of 2 to 97°C and mineralization of 1.47 to 37.14 g/l are studied and compared with surface freshwater from their localities. The δD and δ18O values in surface waters vary from −121.4 to −89.5‰ and from −16.4 to −11.1‰, respectively, while respective values in thermomineral waters range from −134.2 to −92.5‰ and from −17.6 to −10.5‰. The δD value in surface waters decreases from the east to west, i.e., toward interior areas of the peninsula. Hydrothermal springs most depleted in deuterium (δD < −120‰) are localized in the geodynamically active Kolyuchinskaya-Mechigmen Depression. According to the proposed formation model of Chukotka thermomineral waters, their observed chemical and isotopic characteristics could result from the mixing (in different proportions) of surface waters with the deep-sourced isotopically light mineralized component (δD ≈ −138‰, δ18O ≈ −19‰, M = 9.5−14.7 g/l). The latter originates most likely from subpermafrost waters subjected to slight cryogenic metamorphism.