Synchrotron white beam X-ray topography has been used to characterise bulk crystal defects of thick vapour grown CdZnTe crystals. Whole 50 mm diameter wafers with thicknesses in the range of 2-3 mm were sliced from boules grown by the multi-tube physical vapour transport method and analysed by diffraction topography in a transmission geometry. A variety of defects were observed including cracks, voids and grain boundaries. The largest quantity of defects observed were sub-grains appearing as localised increased intensity in the topographs. The periphery of the wafers showed the highest number of defects, whereas central regions where largely defect-free. We failed to observe any inclusions or precipitates within these crystals. Surface damage from wire-saw cutting was also observed on poorly processed wafers: these defects were otherwise invisible to standard characterisation methods. X-ray topography has proven to be a useful tool for non-destructively investigating bulk extended defects in CdZnTe crystals for radiation detector applications. (C) 2012 Elsevier B.V. All rights reserved.