A surgical stapling instrument suitable for performing a gastrointestinal anastomosis is provided. The stapling instrument incorporates a jaw clamping mechanism which applies clamping forces to its jaw members to resist the forces exerted on the anvil and staple cartridge carrying portions of the jaw members when the staples are formed. Preferably, the stapling instrument includes a pair of elongate jaw members, one of which supports a staple cartridge adapted to receive at least two laterally spaced longitudinal rows of staples, and the other provided with an anvil adapted to form the staples. A pusher bar and knife blade assembly is slidable longitudinally relative to the jaw members to sequentially drive the staples from the cartridge and form the staples against the anvil to produce a pair of laterally spaced rows in the tissue. The pusher bar and knife blade assembly includes a knife blade for cutting the tissue along a line between the longitudinal staple rows. A latching mechanism is provided for latching the jaw members together at an intermediate position therealong adjacent to the staple cartridge and the anvil. In addition, a cam mechanism is provided for urging the jaw members apart at a position remote from the latching mechanism to resist the forces exerted on the staple cartridge and anvil when the pusher bar and knife blade assembly is actuated to staple and cut the tissue gripped between the jaw members.