Low temperature fast-atom bombardment study of frozen D2O–NaCl solutions gave results similar to those obtained earlier for the H2O–NaCl system. Thus, sets of clusters (D2O) n•D+, (D2O) n•Na+, (D2O) n•NaCl•Na+, (NaCl) m•Na+ with a characteristic distribution depending on the composition of the sample and phase transitions on its thawing were recorded. A typical cluster pattern, attributed in the case of the H2O–NaCl system to a phase of a crystalline hydrate NaCl•2H2O, was observed for the D2O–NaCl system as well. At the same time, recently available reference data on the solubility of NaCl do not contain a specification for the formation of a crystalline hydrate on cooling of NaCl solution in D2O. Considering the present mass spectrometry data, the possibility of incorporation of heavy water into NaCl crystalline hydrates is discussed.