The present application relates to a method for determining the position or relative position of body parts, taking into account the anatomical symmetry, wherein at least one first-side body part is provided on the first side of an anatomical body, and at least one second-side body part is provided on the second side of the anatomical body, wherein the first side is separated from the second side by a body symmetry plane, said method comprising the steps of: providing first-side body part data which describes or implies the position of the at least one first-side body part; providing second-side body part data which describes the position of the at least one second-side body part; providing symmetry plane data which describes the position of the body symmetry plane; calculating the mirrored position or mirrored positions of the at least one second-side body part which results after the position of the at least one second-side body part has been mirrored on the body symmetry plane, on the basis of the second-side body part data and the symmetry plane data, and determining and/or displaying a deviation between the mirrored position or positions of the at least one second-side body part and the position or positions of the at least one first-side body part; and/or determining a mirrored relative position of the second-side body parts, on the basis of the second-side body part data and the symmetry plane data.