We have carried out the first-principles total energy calculations to investigate the structural properties of ZnO, we report total energy calculations for ZnO in the B4 (wurtzite), B3 (zinc blende), B2 (cesium chloride), and B1 (rocksalt) crystal structure over a range of pressure and we present a description of the transition phases of ZnO. The calculations are based on the density functional theory and we have used both the generalized gradient approximation (GGA) and local density approximation (LDA) for the exchange and correlation potential. Our results for transition pressures and equilibrium lattice parameters as well as their dependence on pressure were compared with experimental data and previous calculations. (C) 2007 Elsevier B.V. All rights reserved.