This research,uas concerned with the theoretical investigation of the spray issued from a pressurized metered-dose inhaler (pMDI). The theoretical investigation of the pMDI spray consisted of constructing a model of the fluid flow through the pMDI that was based on a quasi-steady-state separated flow analysis during a single actuation and included a qualitative and quantitative description of Me primary atomization process, the resultant spray model being calculated from the solution of the multiphase transport equations using the discrete droplet model (DDM). The predicted results were validated against detailed temporal and spatial experimental data obtained using phase Doppler particle analysis (PDPA).