An embedded cluster analysis of the lattice distortions induced by As3+, Sb3+, and Bi3+ substitutional impurities in crystalline KCl is presented. Active clusters containing more than 100 atoms that are embedded in a quantum representation of the crystalline environment are used. Charge compensation is achieved by introducing two cation vacancies in the host lattice, both in nearest-neighbor (NN) and next-nearest-neighbor (NNN) configurations. Distortion trends as a function of the impurity cation size are identified and discussed, as well as the relative stability of the. NN and NNN configurations.