An orthosis for a vacuum treatment of the deformations of the thorax, said orthosis configured to be pressed against the thorax along a direction extending from the head to the feet, having the general shape of an open box applied against the thorax and having a bottom wall, a peripheral lip made of a flexible and elastically deformable material, extending around the bottom wall and capable of coming into sealed contact against the thorax, to form a vacuum treatment space, said space communicating, by at least one tip for connecting to a flexible pipe, to a means generating a vacuum, wherein the bottom is formed by hollow and rigid juxtaposed compartments, linked to each other by bridges made of the same flexible material as the peripheral lip, the bridges giving the bottom wall a possibility of deformation such that the orthosis is shaped to the anatomy of the thorax when the orthosis is applied vertically against the thorax.