A process for the catalytic conversion of aromatic fractions additionally containing variable proportions of C.sub.5 to C.sub.11 non-aromatic hydrocarbons, to obtain substantially pure benzene and hydrogen, by water dealkylation of the aromatic hydrocarbons and simultaneous reforming of the non-aromatic hydrocarbons, characterized in that aromatic fractions having boiling points which may be varied depending on the yield of hydrogen desired, are treated by steam at temperatures from 350.degree. C. to 600.degree. C., at a pressure of 1 to 80 bars, a volume of liquid passed per unit volume of catalyst of 0.1 to 10 and a water/hydrocarbon charge flow rate ratio of 0.2 to 4, in the presence of a dealkylation catalyst selected from at least one group VIII metal, on a support selected from a sieve L, a pretreated gamma alumina, and a mixed spinel (M.sub.x M'.sub.1-x) Al.sub.2 O.sub.4, M being a non-noble group VIII metal, and M' being selected from the group consisting of magnesium, manganese, and copper.