The conditions for preparation of high surface area zirconia were studied. Samples were prepared by precipitation from aqueous solutions of zirconium chloride with ammonium hydroxide. The order of addition of the reactants was found to affect the surface area. Digestion of the hydrous zirconia is the key to high surface area zirconia without the necessity of adding other oxides or dopants. Both the temperature and the time of digestion are important parameters. Zirconia with surface area in excess of 220 m(2)/g after calcination at 500 degrees C have been obtained. The materials maintained a surface area of > 90 m(2)/g even after heat treatment at 900 degrees C for 12 h. In addition, digestion led to the formation of the tetragonal allotrope of zirconia. Samples which had been digested for long times at 100 degrees C are tetragonal and maintain this phase up to 1000 degrees C. The effects of digestion seems to be related to a phase transformation of the hydrous precursor at around 80 degrees C. A mechanism based on defect density is postulated to explain the phase stability.