In this paper, a creep-damaged material is modelled as a two-phase composite material comprising a matrix containing a distribution of clustered spherical voids. The voids are dispersed uniformly within oblate ellipsoidal regions that represent preferred regions of voiding that can form close to grain boundaries orthogonal to the loading. In turn, the ellipsoidal regions have a preferred direction of alignment and are distributed randomly in the matrix. A double composite model based on coherent elastic wave propagation is used to determine the effective dynamic stiffness of the two-phase material. As the creep progresses, the ellipsoidal elements are sparsely scattered in the matrix, but they continue to grow in volume, containing progressively more voids within them. This evolution results in an anisotropy increase due to the preferential void formation within the ellipsoid elements and alignment of the ellipsoids. The model predicts elastic softening and the development of anisotropy, providing bulk-average information pertinent to the assessment of creep damage. The predicted velocity evolution is in satisfactory agreement with the observations of Morishita and Hirao. (C) 2011 Elsevier Ltd. All rights reserved.