A method is for manufacturing a plurality of hollow reinforcement structures for panels (P) or aerostructures. The method includes the following consecutive steps: a) positioning at least one mandrel on the surface of a panel (P) in correspondence to each hollow structure to be manufactured; b) laminating at least one composite material layer on top of each mandrel; c) polymerizing the panel (P) on which the at least one composite material layer is applied; d) removing the at least one mandrel from the hollow structures. At least two of the hollow reinforcement structures intersect one another. A single polymerization step b) is provided for all the hollow reinforcement structures.