Ceramics have been successfully used for more than twenty years for orthopaedic prostheses, as articulating bearing surfaces against ceramic or polymer components. In both cases, ceramics are characterized by low friction coefficient and low wear rate, compared to metallic materials (stainless steels, titanium and chromium-cobalt alloys). However, their brittleness is much higher than that of metals and presently restricts the use of ceramics for hip joint balls or knee condyles. In the material science field, it is very well known that the association of two different materials can lead to new materials, often called 'composites'. Their properties can be higher than the same properties of each of the individual materials, when taken separately. Nevertheless, the word 'composites' is not universally used with the same meaning. For this reason, we will first give a few definitions in order to clearly understand what can be called 'composite' for ceramic materials. Dispersed phases increase the fracture toughness and high temperature mechanical behaviour of ceramics. In this paper, devoted to medical applications, only mechanical properties at the low (body or room) temperature are analysed. Particular attention is given to the alumina-zirconia system, because aluminium and zirconium oxides are currently accepted as biomaterials for joint prostheses. Finally, a highlight is given on the difficulties in the technological processes to obtain improved ceramic composites.