The local increase of dynamic stress and strain in a flat plate at a sharp change of section is examined by assuming that the bending wave field is diffuse. First, the stress due to a bending wave incident from one direction is determined and then it is determined as if bending waves arrived from all directions in a diffuse field. Theoretical results are presented for the stress concentration as a function of the change of section. Experimental results are presented which agree well with the theoretical results, and show that results are not extremely sensitive to the assumption of a diffuse bending wave field. It is concluded that the results are in a very suitable form for inclusion into a design method.