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The residual stresses induced by grinding in tetragonalzirconia polycrystals stabilised with 2.5% molar yttria (Y-TZP) have beeninvestigated. Two Y-TZP microstructures have been analysed; one consistsof very fine tetragonal grains, whereas the other exhibits a coarser duplexstructure of cubic and tetragonal grains. It is shown that indentation cracksafter grinding are always shorter than in the annealed condition and thiseffect is much larger for the coarse duplex microstructure. It is also foundthat biaxial flexure strength of ground specimens increases with respect tothat in the annealed condition, in spite of the large number of surfacedefects induced by machining. These findings are analysed by Ramanspectroscopy as well as by X-ray diffraction and related to changes in thenear surface microstructure induced by grinding. The results are discussedwithin a fracture mechanics framework.