Abstract: 5-Fluorobenzoxazinones (I) ##STR1## where R is hydrogen, halogen, C.sub.1 -C.sub.3 -alkyl, or trifluoromethyl, trifluoromethoxy, chlorodifluoromethoxy, difluoromethoxy, tetrafluoroethoxy, trifluoromethylmercapto or chlorodifluoromethylmercapto in the m- or p-position, are prepared by reacting the corresponding benzoxazinone (II) ##STR2## in particular one which is 5-chloro-substituted or 5-bromo-substituted, with a fluoride, in particular potassium fluoride, in the presence or absence of a solvent, by a process in which the reaction is carried out in the absence of water or using previously dried starting materials, and in the presence or absence of a decomposition inhibitor, drying preferably being carried out by treatment with an acid halide, e.g. thionyl chloride, and the inhibitor used being a metal iodide, e.g. sodium iodide, or iodine.