A three-dimensional X-ray cone beam tomograph dedicated to the nondestructive examination of radial Si 3 N 4 ceramic turbine wheels is presented. These wheels have a density of 3.2 g/cm 3 and a maximum diameter and height of approximately 100 mm and 75 mm, respectively. Cone beam tomography may be viewed as the generalization to 3 dimensions of conventional tomography. A 3D numerical image of the entire volume of the object to be inspected is mathematically reconstructed from a set of digital radiographies called projections. Each projection is associated with a specific angular position of the object. The instrument developed by CEA/LETI consists of a 225 kV maximum voltage X-ray source, a two-dimensional X-ray detector based on a converter screen coupled to a cooled CCD camera and a mechanical system allowing the turbine wheel to be rotated. A personal computer triggers the data acquisition and controls the motorized axes. The data are pre-processed and the images are reconstructed on a work station. A total of 750 projections, each one consisting of 900 by 600 pixels coded on 16 bits, have been acquired for the 3D reconstruction of one turbine wheel. The limit of flaw diameter detectability of the instrument is 0.15 mm through 50 mm of Si 3 N 4 ceramic and the geometric resolution after reconstruction is 0.3 mm. All detected flaws may be sized and localized.