The shear-induced particle migration in a polydisperse concentrated suspension is described using migration potentials for the various particle size fractions. The model is applied to solve the flow patterns and the particle concentration distributions in bidisperse suspensions in various viscometric flows. For the case of a continuous particle size distribution a formulation of this model in terms of concentration distribution moments is presented. The model predicts the total migration of the particles in the various flow devices and the size segregation of the various fractions. The calculations capture well the few experimental observations reported so far. It is found that in all calculated cases the total energy dissipation rate and, therefore, the power required to drive the flow were diminished considerably at steady state.