The diffuse X-ray scattering from sodium chloride single crystals has been measured in non-symmetry directions over a range of scattering angles from 20° to 110°. The measured intensities show that no need exists to consider defect diffuse scattering and that excellent agreement is obtained with the calculated intensities, comprising theoretical values of Compton scattering and computed values of thermal diffuse scattering. The first-order, second-order and total values of thermal diffuse scattering have been computed from the eigenvectors and eigenfrequencies of Karo and Hardy. Another approximate method of calculating the higher orders of thermal diffuse scattering intensity, involving only the Debye-Waller factors, is given.