The final correction unit (1) is applied in apparatuses for straightening iron rods and the like, comprising a plurality of contrarotating straightening rollers (3, 4) between which the rods (2) to be straightened are inserted, so that they advance along a longitudinal direction (A). The unit (1) comprises at least one first auxiliary roller (11) and one second auxiliary roller (12), whose axes are parallel to the axes of the straightening rollers (3, 4) and are arranged in series on the same plane as the straightening rollers. An abutment roller (13) is adapted to cooperate with the auxiliary rollers (11, 12) in order to clamp the rods (2) on a mutual tangency plane that is substantially longitudinal to the advancement direction (A). The auxiliary rollers ( 11, 12) can rotate about supporting means (10) that oscillate about an axis that is perpendicular to the plane of the auxiliary rollers (11, 12). Means (31, 32) for adjusting the angular position of the supporting means (10) are adapted to tilt appropriately the plane of tangency formed by the auxiliary rollers (11, 12) with respect to the advancement direction (A) in order to correct the residual curvature of the rods (2).