Single crystals of Czochralski grown Nd:YAG have been observed to crack more frequently during growth as the bulk substitutional Nd concentration is increased. Examination of the fracture surfaces indicated that in some cases the cause of failure was microscopic voids acting as stress concentrators. In other cases, the origin of fracture could not be ascertained directly from observation of the fracture surfaces. High-resolution transmission electron microscope studies of samples taken from the core of boules containing 1.02% Nd suggested that spherical particles rich in Nd may act as sources of stress in these high-Nd-doped YAG crystals. The hydrostatic stress at the particle/matrix boundary has been determined from elasticity calculations to be 80MPa. In boules containing 1.395% Nd, rod-shaped particles were observed throughout the crystal. From electron diffraction analysis these particles appeared to be regions of small misorientation, <1degrees. (C) 2004 Elsevier B.V. All rights reserved.