The purpose of this retrospective study was to evaluate the changes in the upper lip (UL) by posterior impaction and setback (PI-SB) of the maxilla. The samples consisted of 29 skeletal Class III patients (10 men and 19 women) who received bimaxillary surgery including PI-SB of the maxilla after Le Fort I osteotomy. Lateral cephalograms were taken at 1 week before surgery (T0) and 6 months after surgery (T1). After linear and angular changes of the hard and soft tissue variables were measured, the paired t test, Pearson correlation test, and univariate linear regression analysis were performed for statistical analyses. The changes in the hard tissue landmarks were as follows: ANS, U1E, and U6MBC moved backward (P < 0.001, P < 0.001, and P < 0.05, respectively) and upward (P < 0.001, P < 0.01, and P < 0.001, respectively), whereas A point, U1A, and PNS moved upward only (P < 0.01, P < 0.01, and P < 0.001, respectively). In terms of the soft tissue change, although subnasale (Sn) did not show significant change, pronasale (Pn) moved upward (P < 0.05); UL, backward and downward (all P < 0.001); and Stms (stomodium-superius), backward (P < 0.001). There were significant correlations between the horizontal change of the UL and that of A point and U1E (P < 0.01, P < 0.05). The regression equation of the horizontal change of UL and U1E was [INCREMENT]UL-vertical reference line (VRL) = (0.476 × [INCREMENT]U1E-VRL) - 0.581 (P < 0.05). If U1E moves backward by 3 mm and 5 mm, the UL is predicted to move backward by 0.9 mm and 1.8 mm, respectively. These results might provide a guideline in diagnosis and treatment planning for maxillary surgery with PI-SB.