Stability after transverse expansion of the maxilla via Le Fort I osteotomy with segments was evaluated in 39 patients. The average expansion was 5.4 mm at the second molars, decreasing almost linearly to 2.8 mm at the first premolars. Postsurgical relapse also was greatest at the second molars, averaging 2.6 mm. The percentage of relapse was greatest posteriorly, decreasing from 49% at the second molars to 30% at the first premolars. Considerable variability in stability followed surgery: Three-fourths of the patients had some relapse at the first molars (greater than 3 mm in 28%), but one fourth were stable. Sixty-two percent of the patients had a net posttreatment gain in arch width at the first molars. No correlation was found between transverse relapse and the type of presurgical orthodontic tooth movement, the use of rigid fixation, or the use of an auxiliary stabilizing arch wire. The amount of postsurgical relapse was significantly greater in those who had concurrent mandibular surgery. To improve clinical results with surgical expansion, we recommend (1) moderate overexpansion at surgery for major transverse changes, (2) maintenance of the occlusal splint for at least 6 weeks, and (3) use of a lingual arch wire or auxiliary labial arch wire to maintain molar width during postsurgical orthodontics.