A patient positioning apparatus for use with a mattress, the patient positioning apparatus comprising: a first lateral tilt bladder and a third lateral tilt bladder configured to underlie a first side of the mattress, and a second lateral tilt bladder and a fourth lateral tilt bladder configured to underlie a second side of the mattress, in which the tilt bladders are inflatable to alter the position of a patient lying on the mattress; in which inflation and/or deflation of the lateral tilt bladders is controllable by a controller; and in which the first lateral tilt bladder is configured to tilt the patient's sternum towards the second side of the mattress when inflated, the second lateral tilt bladder is configured to tilt the patient's sternum towards the first side of the mattress when inflated, the third lateral tilt bladder is configured to tilt the patient's pelvis towards the second side of the mattress when inflated, and the fourth lateral tilt bladder is configured to tilt the patient's pelvis towards the first side of the mattress when inflated, characterised in that a first check valve is configured to allow fluid communication in one direction from the third lateral tilt bladder to the first lateral tilt bladder, and a second check valve is configured to allow fluid communication in one direction from the fourth lateral tilt bladder to the second lateral tilt bladder, in which each lateral tilt bladder is in fluid communication with a separate inflation port, and in which the first lateral tilt bladder is inflatable without inflating the third lateral tilt bladder, and the second lateral tilt bladder is inflatable without inflating the fourth lateral tilt bladder. a first lateral tilt bladder and a third lateral tilt bladder configured to underlie a first side of the mattress, and a second lateral tilt bladder and a fourth lateral tilt bladder configured to underlie a second side of the mattress, in which the tilt bladders are inflatable to alter the position of a patient lying on the mattress; in which inflation and/or deflation of the lateral tilt bladders is controllable by a controller; and in which the first lateral tilt bladder is configured to tilt the patient's sternum towards the second side of the mattress when inflated, the second lateral tilt bladder is configured to tilt the patient's sternum towards the first side of the mattress when inflated, the third lateral tilt bladder is configured to tilt the patient's pelvis towards the second side of the mattress when inflated, and the fourth lateral tilt bladder is configured to tilt the patient's pelvis towards the first side of the mattress when inflated, characterised in that a first check valve is configured to allow fluid communication in one direction from the third lateral tilt bladder to the first lateral tilt bladder, and a second check valve is configured to allow fluid communication in one direction from the fourth lateral tilt bladder to the second lateral tilt bladder, in which each lateral tilt bladder is in fluid communication with a separate inflation port, and in which the first lateral tilt bladder is inflatable without inflating the third lateral tilt bladder, and the second lateral tilt bladder is inflatable without inflating the fourth lateral tilt bladder.