Abstract: An automated surgical instrument for performing minimally-invasive surgery comprises a rigid cannula having a lumen for receiving a surgical tool at the distal end thereof. The tool can comprise a variety of linkage-operated tools, such as a grasper, clamp or scissor. The tool can also comprise an optical or gas channel. The cannula is supported on a ball-and-socket-type swivel assembly that pivots freely along orthogonal axes. The swivel is mounted on a movable arm assembly that extends and retracts. The arm assembly is mounted to a base that moves the arm assembly from side to side. Pivoting of the cannula occurs in response to movement of the arm assembly along the base and through extension and retraction of the arm.