The solubility data for sodium halides (NaF, NaCl, NaBr, and NaI) have been determined at 298.15 K in the ε-increasing mixtures of water-formamide, water-N-methylformamide, and water-N-methylacetamide. In all cases, the solubility of the electrolytes was decreased significantly in the presence of a cosolvent. The solubility of an electrolyte in a given solvent depends on both the nature of the solvent (mainly the polarity, dielectric constant, solvation, or preferential solvation if the solvent is a mixture of solvents, etc.) and the properties of the electrolyte (principally the size, the charge, and the possible association of its ions). If the molality of saturation is not sufficiently small, the ion-ion and ion-solvent interactions must be considered. Although it was not the objective of this work, the solubility values were qualitatively correlated with several properties of the solvent and solute. Finally, a simple justification, which was both qualitative and quantitative, was carried out.