The attenuation of thermally induced sound waves in benzonitrile has been measured with Brillouin light scattering. The attenuation in solutions of benzonitrile with carbon tetrachloride has also been measured as a function of temperature. Neat benzonitrile and the solutions display a maximum in the Brillouin line width. The spectra are analyzed in terms of an extended hydrodynamic theory which includes the effect of orientational anisotropy on the polarized Rayleigh-Brillouin spectrum. The dispersion in benzonitrile appears to be due to translational-vibrational energy transfer.