The mechanical performance of ceramic materials is highly dependent on the existence of incipient flaws. This paper investigates the relationship between the size of the pre-existing flaw and failure stress for disc-shaped specimens of zirconia bioceramic subjected to an equibiaxial stress field. As the size of initiating flaw increased, the stress under which discs failed decreased, sensibly allowing the fracture toughness of the material to be calculated. The value obtained, 8 MPam(1/2), is in reasonable agreement with previous experience, giving confidence in the validation procedure used and the data obtained. For cyclic loading, periods of stable fatigue crack growth occurred with initial defects extending to reach critical values. Based on data for discs that failed under monotonic loading conditions, it was possible to determine the critical flaw size and hence degree of crack growth necessary for discs to fail from fatigue at a given peak cyclic stress. Predictive constant flaw size fatigue curves showed reasonable accuracy in that the estimated incipient flaw size at a given fatigue life was equivalent to the true flaw size, measured from the fracture surface of failed disc specimens.