The invention relates to a method of preparing an alkylated aromatic compound. The inventive method is characterized in that it comprises an alkylation reaction of an aromatic compound with an alkylating agent which is selected from an olefin, an alcohol and a polyalkylated aromatic compound, in the presence of a catalyst which is a porous crystalline material with the following chemical composition in the calcined form: X.sub.2O.sub.3:n YO.sub.2:m ZO.sub.2, wherein (n+m) is at least 5, X is at least a trivalent element, Z is Ge, Y is at least a tetravalent element different from Ge and the n/m ratio is at least 1. Said method is particularly suitable for obtaining cumene.