Previous measurements of refractive index vs wavelength for cubic zirconia were extended to include the variation of index with Y(2)O(3) stabilizer concentration. It was found that a three-term Sellmeier formula fits the index data for each concentration to within ~1 x 10(-4) and that the Sellmeier constants have a nonlinear dependence on concentration but do follow the density. Fitting each of the six Sellmeier constants to a threeterm polynomial provides a set of eighteen coefficients sufficient to calculate the index at any wavelength, for any concentration. Conversely, the Y(2)O(3) concentration can be determined from the refractive index with greater accuracy than by chemical analysis.