Abstract: A patient support structure including a unit having at least two defined shaped zones (30, 32) inflatable from a deflated condition in order to modify the topography of the support. One of the zones (30) is larger than the other (32) so that inflation of the larger zone lifts a patient to one side (towards the smaller zone 32) and the inflated smaller zone supports the patient and prevents the patient from slipping off the support structure. In a more preferred embodiment, the support structure comprises two units, each having at least two defined shaped inflatable zones (30, 32), the larger zone 30 of each unit being in opposed configuration and the units being inflatable independently of one another so that a patient can be lifted to one side or the other side according to which unit is inflated.