A method for manufacturing a hydropneumatic accumulator including a metal sheet casing and an elastomer membrane which separates the inside of the casing into a first chamber containing a pressurized gas and a second chamber containing a liquid, this membrane being fixed to the casing by a cup, in which method a sheet metal disk is cold deformed in two operations, namely a first operation for obtaining a cylindrical or conical blank, one end of which has a convex bottom and provided with an orifice for filling the first chamber with gas, and a second operation in which, after the membrane has been fixed in the casing by means of the cup, the cylindrical part of the blank is hammered so as to give it a spherical shape with an axial orifice in which a connection is crimped and welded for feeding liquid into the second chamber, wherein said cup is fixed to the bottom of the casing by irremovable means and the first deformation operation is carried out so that the blank has a form such that the membrane may be engaged between it and the cup, clamping of the membrane between the cup and the casing being obtained during the second spherical hammering operation.