The stability and the effect on the soft tissue profile of mandibular advancement with sagittal split osteotomy and rigid internal fixation was studied prospectively in 30 consecutive patients, 17 to 32 years old, who had a distal occlusion. Profile roentgen cephalometric recordings were made immediately before and shortly after surgery as well as 13 months postsurgically. The mean advancement of the mandible 3 to 8 days after surgery was 5 mm. On average, there was only a small increase in the anterior facial height. At the follow-up after 13 months, the advancement of the mandible had, in most cases, partially relapsed so that the median net effect was 70%. In six subjects, however, the mandible had advanced slightly further. The skeletal relapse was partially masked by compensatory movements of the maxillary incisors so that the mean net effect on the overjet was 83%. The amount of relapse was positively correlated to the magnitude of advancement during surgery. Likewise, a postsurgical relapse of the anterior facial height was positively correlated to the magnitude of advancement during surgery. Likewise, a postsurgical relapse of the anterior facial height was positively correlated to the magnitude of the vertical surgical displacement anteriorly and posteriorly. The soft tissue chin closely followed the underlying hard tissue. The mean net effect on the labial fold, however, was smaller, 88% of the mandibular advancement. The net effect on the lower lip was 66% of the advancement of the mandibular incisor.