The continuous crystallization kinetics for lactose have been determined. Specifically, a model incorporating the effects of growth rate dispersion (GRD) on particle dynamics has been employed to determine continuous crystallization kinetics from experimentally determined size distributions. The existence of GRD was verified by the excessive number of fines (< 50 μm) observed. Crystal size distributions were successfully modeled using a two component rate distribution indicating the existence of two distinct types of nuclei. These could be classed as fast-growers (product crystals) and slow-growers (fines). Nucleation and growth kinetics of these populations were determined and compared to other methods of determining kinetics.