Abstract: A surgical instrument (200) comprises a frame (210) and a jaw assembly (220) in the distal region of the instrument (200). The jaw assembly (220) has a generally straight first tissue interface (230), a generally straight second tissue interface (232) and a tissue effector (e.g., one or more generally straight rows of staples and/or a knife). The jaw assembly (220) is adapted to grip tissue of a patient between the first tissue interface (230) and the second tissue interface (232) and to penetrate the gripped tissue by the tissue effector. The first tissue interface (230) can be moved relative to the second tissue interface (232) by means of a moving device. An actuating device is adapted to actuate the tissue effector. Both the first tissue interface (230) and the second tissue interface (232) have a generally wavy shape, the crests and valleys of the first tissue interface (230) generally matching the valleys and crests, respectively, of the second tissue interface (232).