The invention relates to a process for the continuous polymerization of one or more a-olefin monomers of which at least one is ethylene or propylene comprising the steps of: (1) feeding the one or more a-olefins to a vertically extended reactor suitable for the continuous fluidized bed polymerization of one or more a-olefin monomers of which at least one is ethylene or propylene, which reactor is operable in condensed mode, wherein the reactor comprises a distribution plate and an integral gas/liquid separator located below the distribution plate, (2) withdrawing the polyolefin from the reactor (3) withdrawing fluids from the top of the reactor, (4) cooling the fluids to below their dew point, resulting in a bottom recycle stream, (5) introducing the bottom recycle stream under the distribution plate, (6) separating at least part of the liquid from the bottom recycle stream using the integral separator to form a liquid phase and a gas/liquid phase, (7) feeding the liquid phase to an external pipe, (8) adding a solid polymerization catalyst to the liquid phase in the external pipe resulting in the formation of a slurry stream comprising prepolymer and/or polymer and (9) feeding the slurry stream comprising the prepolymer and/or polymer into the reactor above the distribution plate, wherein the prepolymer and/or polymer are present in the slurry stream in an amount of from 0.01 to 99 wt % based on the total slurry stream upon introduction of the slurry stream into the reactor.