The K Auger spectrum of atomic Mg-including the K-LM and K-MM transitions-excited by 3.8 keV electrons has been measured with high resolution. The absolute energies and relative intensities of all normal K Auger transitions and most of the satellite lines due to 3s shake-up, 3s shake-off and 2p shake-off in the initial 1s ionisation process have been determined. The relative intensities of the normal K Auger transitions agree well with recent theoretical calculations of Howat (1978) including CI between the final ionic states as well as between the final (2S) continuum states.