A surgical instrument with articulated jaw structure includes a frame and two jaws. The jaws have proximal portions that are mounted to each other for movement in a substantially parallel relation between a fully open position wherein the jaws are separated for receiving tissue therebetween and an approximated position wherein the jaws are closer together. Preferably, the jaws are in the fully open position when the distal portion of at least of the jaws is located in an extended position and are in the approximated position when the distal portion of the extended jaw or jaws is located in a retracted position. The surgical instrument may further include a detachable knife assembly and knife actuating mechanism.