The invention relates to a process for preparing isocyanates by reacting the corresponding amines with phosgene, optionally in the presence of an inert medium, in which phosgene and amine are first mixed and converted to the isocyanate in a reactor, and in which a reaction gas which comprises isocyanate and hydrogen chloride leaving the reactor is cooled in a quench by adding a liquid quench medium to form a mixture of reaction gas and quench medium as the product stream. The walls of the quench are essentially completely wetted with a liquid.