A mattress assembly for the treatment and prevention of decubitus ulcers and for the treatment of other conditions of the skin and/or underlying tissue. The assembly includes a base support, mattress core disposed on the support and defining a plurality of discrete, air permeable, hydrophobic air cells, and a pair of lateral bolsters disposed adjacent the sides of the mattress core. A top sheet formed of an air and liquid permeable, highly elastic, low friction water wicking material is disposed over the core and bolsters to provide a planar support surface which readily conforms to the irregularities in the topography of the body of a person resting thereon without wrinkling so as to minimize the shear forces acting on the skin and draw moisture away from the skin. A pump or other suitable means is provided for directing air flow through a plurality of controllable valves to and through the cells of the mattress core and top sheet to inflate the cells for supporting a person thereon and maintaining the skin in a properly hydrated condition. A control assembly regulates the air pressure within individual or groups of cells to maintain the contact pressure of the mattress assembly against the skin of a person thereon at a desired level and to facilitate physician and nursing care.