Aromatic hydrocarbons are nitrated by a process in which the aromatic hydrocarbon is reacted in the liquid phase with an oxide of nitrogen selected from NO, N2O3, NO2 and N2O4 and with an oxygen-containing gas stream in the presence of a heterogeneous oxidic catalyst, wherein at least 0.1 mol %, based on the aromatic hydrocarbon, of water is present at the beginning of the reaction.