A lateral positioning device for the variable lateral positioning of a recumbent person, said lateral positioning device comprising the following features: a) at least one actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) acting on a mattress provided as a lying surface for the person, wherein, by means of the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97), the angle (α L, α R) between the transverse axis of the mattress and the horizontal can be varied, b) wherein the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) has at least one air bellows with a right air chamber, a left air chamber and at least one pump for feeding air into the air bellows (4, 8), wherein the right air chamber is designed to rotate the mattress to the left by filling the right air chamber with an amount of air, and wherein the left air chamber is designed to rotate the mattress to the right by filling the left air chamber with an amount of air, c) wherein the air bellows (4, 8) can be placed between the slatted frame and the mattress of a care bed, characterized by: d) at least one sensor (7, 9) having an output signal, which represents the respective angle (α L, α R) between the transverse axis and the horizontal, e) wherein a first sensor having an output signal representing the respective angle (α L) when the mattress is rotated to the left and a second sensor having an output signal representing the respective angle (α R) when the mattress is rotated to the right are provided, f) wherein the first sensor and the second sensor are each formed as acceleration sensors, g) wherein the first sensor and the second sensor are each arranged between the mattress and the air bellows (4, 8), h) at least one electronic control device, which is connected to the first and to the second sensor (7, 9) and to the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) and is designed i) to determine an actual inclined position from the output signal of the first and of the second sensor (7, 9), ii) to adjust the angle (α L, α R) between the transverse axis of the mattress and the horizontal by actuating the actuator in such a way that the actual inclined position is set to a predetermined target inclined position. a) at least one actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) acting on a mattress provided as a lying surface for the person, wherein, by means of the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97), the angle (α L, α R) between the transverse axis of the mattress and the horizontal can be varied, b) wherein the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) has at least one air bellows with a right air chamber, a left air chamber and at least one pump for feeding air into the air bellows (4, 8), wherein the right air chamber is designed to rotate the mattress to the left by filling the right air chamber with an amount of air, and wherein the left air chamber is designed to rotate the mattress to the right by filling the left air chamber with an amount of air, c) wherein the air bellows (4, 8) can be placed between the slatted frame and the mattress of a care bed, d) at least one sensor (7, 9) having an output signal, which represents the respective angle (α L, α R) between the transverse axis and the horizontal, e) wherein a first sensor having an output signal representing the respective angle (α L) when the mattress is rotated to the left and a second sensor having an output signal representing the respective angle (α R) when the mattress is rotated to the right are provided, f) wherein the first sensor and the second sensor are each formed as acceleration sensors, g) wherein the first sensor and the second sensor are each arranged between the mattress and the air bellows (4, 8), h) at least one electronic control device, which is connected to the first and to the second sensor (7, 9) and to the actuator (4, 8, 10, 12, 13, 14, 92, 93, 94, 95, 96, 97) and is designed i) to determine an actual inclined position from the output signal of the first and of the second sensor (7, 9), ii) to adjust the angle (α L, α R) between the transverse axis of the mattress and the horizontal by actuating the actuator in such a way that the actual inclined position is set to a predetermined target inclined position. i) to determine an actual inclined position from the output signal of the first and of the second sensor (7, 9), ii) to adjust the angle (α L, α R) between the transverse axis of the mattress and the horizontal by actuating the actuator in such a way that the actual inclined position is set to a predetermined target inclined position.