Polarization state variations in light diffracted by an ultrasonic wave are considered in the three regimes: Raman-Nath (RN), Bragg (B) and intermediate. The isotropic and anisotropic cases of ultrasonic light diffraction are described and some examples for RN and B diffraction are given. In the intermediate regime the case of acoustically induced anisotropy in isotropic medium (in fused silica) is discussed and some examples of numerical and experimental results for the intensity distributions, polarization ellipticity and orientation angle in the zeroth and first order of diffraction depending on the RN parameter (proportional to the amplitude of ultrasound) are shown for a given Klein-Cook parameter (at a given ultrasound frequency of about 50 MHz).