Motorcycle helmets attenuate head accelerations through cracking and deformation of the outer shell and inner energy absorbing liner. Impacts with non-planar surfaces have been shown to result in more helmet damage and to be associated with an increased risk and severity of head and brain injury. Our goal was to determine the effect of impact surface shape on helmet damage and the resulting head acceleration response. Previously, we characterized the relationship between residual helmet damage and impact energy onto a flat impact surface (DeMarco et al., 2007). Here we continued this research by conducting helmet impacts onto a curbstone anvil. A total of nineteen drop tests were performed with identical motorcycle helmets impacting a flat (n=10 from DeMarco et al., 2007) or curbstone anvil (n=9) at impact speeds of 0.9-10.1 m/s (energy=2-260J). Residual crush was defined as the maximum percent change in helmet thickness, measured from the interior of the inner liner to the exterior of the outer shell, between the pre- and post-impact conditions. A linear relationship (r²=0.90) between maximum crush and impact energy was observed across all impact energies for flat anvil impacts. For curbstone anvil impacts, a bilinear relationship was observed, with one linear region up to 150J (r²=0.99) and another at 180J and above (r²=0.79). Between 150J and 180J, the residual crush decreased about 40% because of hidden deformation at the liner/shell interface related to penetration of the curbstone anvil. The peak linear head accelerations from the curbstone impacts were significantly less than those from the flat anvil impacts (plt;​0.02). Based on these tests, the relationship between residual helmet liner deformation and impact energy depends on the shape of the object being struck by the helmet. These data suggest that incident specific tests using a similar helmet and struck object may be needed to estimate the impact severity of a motorcycle helmet from its post-impact residual crush.