the invention relates to a method for producing a part comprising a hollow body made from a composite material , using preforms , said method including the following steps : a step in which the preforms are disposed around a suitable supporting element such that the coupling edges of each preform overlap , and come into contact , with a coupling edge of another preform ; a step in which the coupling edges of each preform are joined along a seam ; and a step in which the supporting element is removed and a mold core is inserted in its place before the assembly is placed inside a mold and resin is injected using an rtm / lri method , prior to the polymerization of said resin .