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A combined experimental and theoretical investigation into the vibrational properties of cubic 8-9 mol% yttria-stabilized zirconia (YSZ) is presented. Measurements of acoustic phonon dispersion curves have been obtained from inelastic neutron scattering investigations using a triple axis spectrometer, as well as calculations of the vibrational density-of-states (vDOS) using density-functional theory. The present measurements agree closely with, and extend, previously published results. The phonons become broader and decrease in intensity as the Brillouin zone boundary is approached, particularly in the Γ-Δ-X direction. Interestingly, there is evidence of a previously unreported low energy phonon band (8-9 meV) in the Γ-Σ-X direction, which could possibly be related to the stabilization (by yttria doping) of the imaginary mode of cubic ZrO 2 about the X-point. Compared to pure cubic ZrO 2 , the vDOS of YSZ are broader and extend to higher frequency. Furthermore, the prominent Zr-related feature in the vDOS of c-ZrO 2 at E14 meV is shifted to higher energy in the vDOS of YSZ. This behavior is consistent with the measured dispersion bands (first acoustic branch in the Γ-X direction, about the X-point) of YSZ which is higher in energy by a similar amount relative to that of c-ZrO 2 , thus providing support for the structural model considered.