This paper reports neutron diffraction data and its analysis that characterise a biocompatible hydroxyapatite composite material. The neutron data has elucidated the crystal structure, and enabled the positions of the hydrogen atoms to be determined. The data also shows the improvement of crystallinity during the heat treatment process. An extension of the work involved looking at a hydroxyapatite – carbon nanotube composite material, and neutron diffraction has shown that the retention of the carbon nanotubes in the composite material has been successful. The nanotubes have had no affect on the hydroxyapatite structure.