An ab initio constant pressure technique is applied to study the pressure-induced phase transition in AIN. A first-order phase transformation from the wurtzite structure to a rocksalt structure is observed in the constant pressure simulations. The transformation proceeds via two fivefold coordinated intermediate states within P6(3)/mmc and Cmcm symmetry. The influence of pressure on the electronic structure of AIN is also investigated. The computed pressure coefficients and deformation potential are in good agreement with the earlier first principles calculations. (C) 2009 Elsevier B.V. All rights reserved.