Purpose: The purpose of this study was to investigate the changes in and stability of the maxilla and soft tissue profile achieved after the application of distraction osteogenesis (DO) by use of rigid external distraction (RED) with a retention plate system in unilateral cleft lip and palate (UCLP) adult patients. We compared 2 treatment methods in the management of maxillary hypoplasia: Le Fort I osteotomy and DO. Materials and Methods: Six UCLP adult patients who underwent treatment with the RED retention plate system were examined (DO group). Changes in the positions of soft and hard tissue landmarks were calculated from lateral cephalograms taken before distraction, at the removal of the halo, and 1 year after surgery and were compared with those in 7 other UCLP patients who underwent Le Fort I osteotomy (LF1 group). Results: The mean maxillary advancement was significantly larger in the DO group than in the LF1 group after distraction. During the follow-up period, the relapse rate of the maxilla was significantly smaller in the DO group. An undesirable labial inclination of the upper incisors was found in the LF1 group, which may have been due to relapse. The DO group tended to have a higher soft tissue-to-hard tissue anterior movement ratio from the time of distraction to follow-up. Conclusions: The RED retention plate system improved the midfacial profile by advancement of soft and hard tissue and minimized the risk of injury to the upper lip. Using the RED system with retention plates prevented the undesirable labial inclination of upper incisors that was found in the LF1 group.