Abstract Recent work has shown that calculations of formation energies of Schottky defects in NaCl structure alkali halides using the Born ionic model give good agreement with experiment. Moreover, so long as the Van der Waals interactions are included explicitly the simple Born-Mayer experimental form of repulsive potential is adequate. The same model is here applied to the CsCl-structure alkali halides. The results are contrasted with those for the NaCl alkali halides and the general conclusion is the same, namely that reasonable agreement with experiment is obtained, the theoretical values perhaps being a little low. However, the experimental picture is still far from clear for these salts.