Abstract: An overlay mattress has a plurality of internal elevating means, such as inflatable bladders, for raising selected portions of the mattress to achieve a wide range of patient positions. A fluid such as air may be supplied from a conventional surgical room air supply, a compressed canister, or a compressor to inflate the bladders. A fluid distribution system controls the flow of fluid to desired bladders. The overlay mattress may be used in conjunction with conventional surgical tables and mattresses. A thermal control means is also included in the overlay mattress to regulate a patient's body temperature. A pressure shifting means is also included to reduce the risk of bedsore formation.