A surgical stapling instrument suitable for performing a gastrointestinal anastomosis. 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 of formed staples in tissue gripped between the jaw members and to cut the tissue along a line between the staple rows. A latching mechanism is operable to a partially latched position in which the jaw members are loosely connected together to permit the staple cartridge and anvil to be adjusted in position on the tissue without disconnecting the jaw members from each other. 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. The cam mechanism is initially held in an inoperative position and subsequently held in an operative position when the pusher bar and knife assembly is actuated. Preferably, the staple cartridge is disposable.