A constant pressure ab initio technique is used to study the pressure-induced phase transition in BeO. A first order phase transition from the wurtzite structure to a rocksalt structure at 700.0 GPa is successfully observed in the constant pressure simulation. The wurtzite-to-rocksalt transformation is based on two fivefold coordinated intermediate states with space groups P6(3)/mmc and Cmcm, similar to what has been observed or proposed in various wurtzite structured materials. This phase transition should occur around 70 GPa from the enthalpy calculations. (C) 2008 Elsevier Ltd. All rights reserved.