The paper treats the application of laser to repair of cracks occurring at dies for die casting of non-ferrous metals (particularly aluminium, magnesium and their alloys). The first part describes a suitable laser unit enabling crack grooving and then welding. An Nd:YAG laser source is shown with its equipment for laser-beam transfer, control and directing of laser-beam focus. Dies for die casting are made of quality steels and are of very complex shape. As far as their repair is concerned this means that they are to be welded at their edges, corners, narrow gaps and vertical walls, i.e. in various positions and in various directions. In the second part the grooving technology is described, and in the third part laser welding of grooved cracks using a filler material, i.e., a thin welding wire. At the end some conclusions are drawn. It is stated that from the viewpoints of technology and economics, it is sensible to laser groove and then weld the thermal cracks with a suitable material. The filler material should have such a chemical composition that after welding a weld having adequate mechanical properties, without any additional heat treatment, is obtained.