The electronic structure, the charge density and the total energy of BeS in the rocksalt (B1), cesium chloride (B2), zincblende (B3), wurtzite (B4) nickel arsenide (B8 1 ) and iron silicide (B28) structures are studied using first-principles self-consistent local-density calculations in a large plane wave basis employing soft non-local pseudopotentials. The zincblende structure is the calculated ground state with a = 4.773 B 0 = 101.9 GPa and B 0 = 3.70. The experimental value is a = 4.85 . The wurtzite structure is energetically very close to the zincblende structure. The difference at the minimal energy in these two structures is only 6.2 meV. At a pressure of 58 GPa we observe a transition to the six-fold coordinated nickelarsenide structure. From that structure on no other transition is found to any of the calculated structures.