Abstract: A lateral tilting device for a patient lying on a mattress is capable of being inserted between the mattress and a level bed base or bed frame on which the mattress rests. The lateral tilting device comprises at least two independent first and second inflatable cells, pneumatically independent and positioned at least partly symmetrically from one another in relation to a median axis of the tilting device. The lateral tilting device includes two ‘U’ shaped inflatable compartments that are fitted into one another. A method for the lateral tilting of the mattress includes inflating a said first or second cell and concomitant deflation of the other second or respectively first cell of the tilting device laid out under the mattress.