Surgical instrument for use in a knee joint replacement operation, having a reference block with a proximally oriented block rear face which is configured to bear on a distal end face of a resected femur, a stylus which is arranged on the reference block in the region of an anterior block upper face thereof and has a stylus tip which protrudes proximally beyond the block rear face and is configured to bear on an anterior face of the femur, two reference feet (300, 400) which are spaced apart mediolaterally from one another and are each arranged on the reference block in the region of a underside thereof lying posteriorally opposite the block upper face and each have an anteriorally oriented foot upper face (301, 401) protruding proximally beyond the block rear face, wherein the foot upper faces (301, 401) are arranged in a common reference plane and are each configured to bear on a posterior condyle (KL, KM) of the femur, at least two reference bores (107, 108) which each extend orthogonally to the block rear face continuously from the latter as far as a distally opposite block front face and are each configured for receiving a reference pin which can be introduced into the distal end face of the femur, wherein the at least two reference bores (107, 108) are spaced apart from one another along a virtual spacing line which is elongate mediolaterally and parallel to the reference plane, wherein there is at least one compensation element which is configured for form-fitting and/or force-fitting releasable connection to one of the two reference feet (300, 400), and wherein the at least one compensation element has an anteriorally oriented element upper face which comes to bear, instead of the relevant foot upper face (301, 401), against the relevant posterior condyle (KL, KM), characterized in that the at least one compensation element has, on its element underside, a receiving pocket which is sunk anteriorally and is open posteriorally and in which the reference foot (300, 400) can be received in a form-fitting manner. a reference block with a proximally oriented block rear face which is configured to bear on a distal end face of a resected femur, a stylus which is arranged on the reference block in the region of an anterior block upper face thereof and has a stylus tip which protrudes proximally beyond the block rear face and is configured to bear on an anterior face of the femur, two reference feet (300, 400) which are spaced apart mediolaterally from one another and are each arranged on the reference block in the region of a underside thereof lying posteriorally opposite the block upper face and each have an anteriorally oriented foot upper face (301, 401) protruding proximally beyond the block rear face, wherein the foot upper faces (301, 401) are arranged in a common reference plane and are each configured to bear on a posterior condyle (KL, KM) of the femur, at least two reference bores (107, 108) which each extend orthogonally to the block rear face continuously from the latter as far as a distally opposite block front face and are each configured for receiving a reference pin which can be introduced into the distal end face of the femur, wherein the at least two reference bores (107, 108) are spaced apart from one another along a virtual spacing line which is elongate mediolaterally and parallel to the reference plane, wherein there is at least one compensation element which is configured for form-fitting and/or force-fitting releasable connection to one of the two reference feet (300, 400), and wherein the at least one compensation element has an anteriorally oriented element upper face which comes to bear, instead of the relevant foot upper face (301, 401), against the relevant posterior condyle (KL, KM), characterized in that the at least one compensation element has, on its element underside, a receiving pocket which is sunk anteriorally and is open posteriorally and in which the reference foot (300, 400) can be received in a form-fitting manner.