Direct particle sizing of colloidal suspensions at high solid concentrations is difficult due to confounding effects of multiple scattering and particle interactions. In this work, the frequency domain photon migration (FDPM) technique, based upon multiple light scattering, is extended for particle sizing of colloidal suspensions at high volume fractions by combining an appropriate model to account for particle interactions. FDPM measurements of isotropic scattering coefficients were conducted to assess the effect of particle interactions of polydisperse polystyrene samples at high volume fractions ranging from 1% to 40%. The isotropic scattering coefficients were then compared with the theoretical predictions which include the full polydisperse hard sphere Percus-Yevick (HSPY) model as well as the decoupling approximation and the local monodisperse approximation models to account for excluded volume effects. Results show that the polydisperse HSPY model is suitable for accounting for particle interactions which predominately arise from volume exclusion effects and which influence light scattering. Upon use of the polydisperse HSPY model to predict static structure factors, the particle size distribution (PSD) of polydisperse polystyrene suspensions was recovered at high volume fractions up to 40% at two different wavelengths. Our inversion results agree well with PSD measured by dynamic light scattering at a diluted sample of the same suspensions (similar to0.01% volume of solids).