The microstructure of nitrogen implanted AISI 302 austenitic stainless steel and the effect of long-term room temperature ageing on it have been studied. Samples were implanted in 1992 with 2.5 x 10(21) N-2(+) m(-2) at 130 keV The characteristics of the implanted layer and the depth profile have been investigated by scanning transmission electron microscope combined with energy dispersive X-ray spectrometry. Electron diffraction patterns recorded in the implanted layer using transmission electron microscopy confirm the formation of CrN along with the presence of Cr2N. The identification of phases by glancing angle X-ray diffraction also indicates the formation of Cr2N and nitrogen solid solutions. The effects of ageing on the microstructure are observed to be small. (C) 2003 Elsevier B.V. All rights reserved.