The invention relates to a method for the preparation of isocyanates. Here it is provided that (i) a first organosilicon compound having at least one silicon atom Si.sup.1 and a unit of formula G-I bound thereto ##STR00001## is converted to a third organosilicon compound having a unit of formula G-II ##STR00002## by silylation of the NH group of the unit of formula G-I with a second organosilicon compound having one silicon atom Si.sup.2; and (ii) the third organosilicon compound is reacted to an isocyanate by thermolysis, whereby the unit of formula G-II is converted to an isocyanate group.