Abstract: A device for positioning a patient who is to undergo a lumbar puncture in particular a device having a plane of so-called sagittal symmetry, comprises a rigid or semi-rigid cushion that includes: a placing surface provided with an anterior edge and resting on the patient's thighs, a front leaning surface for the patient's abdomen and thorax, rising above the placing surface from the anterior edge and having a convex profile in the plane of sagittal symmetry to position the patient's spine in kyphosis, this front leaning surface, opposite the anterior edge, leading into a housing for supporting and laterally centring the patient's head, centred along the plane of sagittal symmetry, and two side faces in which a clasping surface opens oriented in opposite direction to the front leaning surface to allow at least part of the upper limbs to clasp the cushion against the patient's abdomen and thorax.