A surgical access device is adapted to facilitate access through an incision in a body wall having an inner surface and an outer surface, and into a body cavity of a patient. The device includes first and second retention members adapted to be disposed in proximity to the outer surface and the inner surface of the body wall, respectively. A membrane extending between the two retention members forms a throat which is adapted to extend through the incision and form a first funnel extending from the first retention member into the throat, and a second funnel extending from the second retention member into the throat. The throat of the membrane has characteristics for forming an instrument seal in the presence of an instrument and a zero seal in the absence of an instrument. The first retention member may include a ring with either a fixed or variable diameter. The ring can be formed in first and second sections, each having two ends. Couplings can be disposed between the ends to accommodate variations in the size of the first retention member. The first retention member can also be formed as an inflatable toroid, a self-expanding foam, or a circumferential spring. A plurality of inflatable chambers can also provide the surgical access device with a working channel adapted for disposition across the body wall. A first retention member with a plurality of retention stations functions with a plurality of tethers connected to the membrane to change the shape of the membrane and the working channel. A stabilizing platform can be used to support the access device generally independent of any movement of the body wall.