Co-precipitated yttria-stabilised zirconia powders were doped with 0.05% wt of copper oxide (CuO). Samples were sintered at 1300degreesC-1325degreesC with holding times varying from 12 mins up to 4 hrs. The material was stable when exposed to hydrothermal ageing at 180degreesC, with only minimal signs of degradation in many cases for in excess of 3000 hrs. Excellent ageing resistance was observed for samples doped with 0.05 wt% of CuO, sintered at 1315degreesC for 12 mins which developed less than 1% monoclinic phase content, after 5000 hrs. Samples doped with 0.05 wt% of CuO, sintered at 1325degreesC for 12 mins, developed more than 50% of surface monoclinic phase content after 800 hrs of ageing, maintaining the same amount of monoclinic phase content for in excess of 3000 hrs. Plain samples sintered at 1325degreesC for 2 hrs developed more than 30% monoclinic phase content after 750 hrs. Doping with CuO improved the ageing resistance of the samples sintered at 1300degreesC-1315degreesC for 2 hrs and 12 mins holding times respectively.