PURPOSE: The aim of this study was to evaluate the skeletal and dentoalveolar dimensional changes following surgically-assisted rapid maxillary expansion (SARME). PATIENTS & METHODS: Thirteen adults who had been treated by SARME for transverse maxillary deficiency from May 2000 to December 2003 were evaluated. The SARME procedure was the subtotal Le Fort I osteotomy combined with pterygomaxillary separation and anterior midpalatal osteotomy. Dental study casts and posteroanterior cephalometric radiographs were taken before operation, after removal of expansion device, and follow up period. Nasal cavity width, skeletal and dentoalveolar parameters were measured pre- and post-operatively. RESULTS: 1. Mean nasal cavity width was increased 12%(0~21%) of total expansion after retention. 2. Mean maxillary interdental width was increased 70%(47~99%), 95%(84~115%), and 77%(57~94%) of total expansion in the canine, the first premolar, and the first molar region, respectively after retention. 3. Mean maxillary alveolar bone width was increased 66%(42~84%), 74%(42~94%), and 57%(31~78%) of total expansion in the canine, the first premolar, and the first molar region, respectively after retention. 4. Mean palatal vault depth was decreased 1.3 mm (0.5~2.0 mm) after retention. 5. Mean interdental and alveolar bone width of the mandibular canine and intermolar width of mandible were slight increased as maxilla was expanded after retention. 6. There were statistical differences between preoperative and postoperative values of nasal cavity, all maxillary interdental and interalveolar widths, palatal vault depth, mandibular interdental and interalveolar width of canine(paired t-test, p <0.05). 7. The maxillary interdental and alveolar bone width were decreased approximately 25% of total expansion by relapse at follow up period. CONCLUSION: In conclusion, most amounts of maxillary interdental expansions were acquired with the expansion of the maxilla by SARME. For preventing the relapse, approximately 25% of the overexpansion was needed.