Microstructural features and mechanical properties of friction stir welded (FSW) EN AW 5083 H111 plates were investigated. Friction stir welding led to the fragmentation of coarse Al-6(Mn,Fe) particles, the dissolutionising of fine Al3Mg2 particles and to recrystallisation across the nugget zone (NZ), producing hardness profiles that show little or no variation across the joint. The joints produced at a welding speed of 80 mm/min were larger than those produced at 125 mm/min. The shape of the joint, on the other hand, was dictated by the pin profile. Joints produced by the threaded circular pin invariably revealed elliptical NZs while the NZs of the joints produced by the triangular pin were basin-shaped. The welding speed also had an impact on the NZ grain size and the tensile properties of the joint. The NZ grain size was smaller, the ultimate tensile strength (UTS) and the elongation values were higher at a welding speed of 80 mm/min than at 125 mm/min for both pin profiles. The superior tensile properties at the lower welding speed were consistent with the smaller grain size and bigger joints in the former. The joint efficiency of the EN AW 5083 plates welded with a triangular pin at a tool rotation rate and welding speed of 800 rpm and 80 mm/min, respectively, was estimated to be as high as 97%.