A method of casting a hollow hip prosthesis head comprises forming a wax pattern of a femoral head including two cores. The first is a central socket-forming core and the second a ceramic hollow-forming core. The wax pattern is coated with a ceramic slurry to form a shell in which core extensions are captivated. The wax is melted and evacuated and the shell is fired to form a mould. Metal is cast and, when cool, the shell and cores are removed and each aperture formed in the head by the hollow-forming core is sealed.