This invention relates to a process and an installation for treatment of a heavy petroleum feedstock, of which at least 80% by weight has a boiling point of greater than 340° C., whereby the process comprises the following stages: (a) hydroconversion in a boiling-bed reactor operating with a rising flow of liquid and gas, conversion in % by weight of the fraction having a boiling point of greater than 540° C. being from 10 to 98% by weight; (b) separation of the effluent obtained from stage (a) into a gas containing hydrogen and H2S, a fraction comprising the gas oil and optionally a fraction that is heavier than gas oil and a naphtha fraction; c) hydrotreatment by contact with at least one catalyst of at least the fraction comprising the gas oil obtained in stage (b); d) separation of the effluent obtained at the end of stage (c) into a gas containing hydrogen and at least one gas oil fraction having a sulfur content of less than 50 ppm, preferably less than 20 ppm, and more preferably less than 10 ppm, the hydroconversion stage (a) being conducted at a pressure P1 and the hydrotreatment stage (c) being conducted at a pressure P2, the difference ΔP=P1−P2 being at least 3 MPa, hydrogen supply for the hydroconversion (a) and hydrotreatment (c) stages being ensured by a single compression system with n stages.