The coefficient of linear thermal expansion (&agr;) for NaCl has been determined from 50°C to near the melting point (800°C) with an automatic recording dilatometer. The results confirmed the authors' suspicions that the values of &agr; reported by Eucken and Danno¨hl are systematically high above 450°C. The experimental data are not satisfactorily represented by polynomial curves from the first through the eighth order as there is a decided increase in the thermal expansion above 600°C. Consequently, two second‐order polynomials are employed to adequately fit the data. The difference (&Dgr;&agr;) at constant temperature between the high‐temperature polynomial and the extrapolation of the low‐temperature polynomial behaves logarithmically with respect to 1/Tat high temperatures. The slope of this curve corresponds to a formation energy of 1.916 eV, which compares favorably with the energy required to form a pair of isolated positive and negative ion vacancies within the crystal (a Schottky defect).