A lateral device (3) for tilting a patient (20) lying on a mattress (10), and capable of being inserted between said mattress and a level bed base or bed frame (11) on which said mattress rests. The lateral tilting device comprises at least two independent first and second inflatable cells (1, 2), pneumatically independent and positioned at least partly symmetrically from one another in relation to a median axis (XIX1) of said tilting device, A support device comprises a mattress capable of supporting a patient in a reclining position and the lateral tilting device under the mattress, A method for the tilting of the mattress (10) comprises inflating one of the cells (1, 2) and concomitant deflation of the other cell (2, 1) of said tilting device (3).
