The authors report results of a relativistic ab initio band-structure calculation via the KKR method for the SmS compound with the NaCl structure in the low-pressure phase. The exchange potential was taken in the free-electron Slater approximation. They have solved the full Dirac equation in the interior of the 'muffin tin' spheres. The energies were evaluated at several symmetry points and other general points in the 1/48 wedge of the FCC Brillouin zone. The energy band obtained indicates a gap throughout the whole BZ. The most excited valence bands are f-like and energetically located immediately below the conduction band. The electronic structure is discussed in terms of the proposed models for the understanding of the unusual properties of this compound.