During the course of an ongoing study into the impact and erosion properties of alumina by the US Bureau of Mines, it was discovered that specimen thickness had a significant effect upon certain fractographic observations. To quantify this effect, impact studies were carried out on 1.9, 3.1 and 10.0 mm thick Al2O3 (alumina) discs. These discs were impacted at velocities from 15 to 65 m s(-1) using 1.69 mm-diameter WC-Co spheres. In conjunction with this experimental approach, finite element models of the impact couples were constructed for the 1.9 and 10.0 mm-thick alumina discs. An elastic/plastic analysis was performed of the impact event in each case. Experimental and numerical results indicate that the length, depth and geometry of radial cracks are strongly dependent upon specimen thickness.