The cyclic fatigue life of zirconia bioceramic was determined under biaxial flexion using disk-shaped specimens. The fatigue life was not reduced by subjecting the material to a simulated. physiological environment nor was it affected by testing at different loading frequencies. Tests performed at different stress ratios produced a large degree of scatter in the data but a statistical analysis proved that there was no significant effect on the fatigue life of the material. Failure of disk specimens was initiated either by flaws introduced during manufacturing or by the more typical inherent flaws commonly observed in ceramics. The former generally resulted in premature, low-stress failures on initial loading whereas the latter acted as initiating defects for fatigue cracks that then propagated to failure. The distributions of the two categories of flaw were analyzed using two- and three-parameter Weibull probability functions. It became clear that the Weibull modulus for the fatigue failures was consistent with previously reported work. on other ceramics.