Objective: To compare the effects of rapid maxillary expansion (RME) and surgically assisted rapid maxillary expansion (SARME) on dentoalveolar structures following orthodontic treatment, as well as stability at 2-year follow-up. Materials and Methods: Two groups of subjects were used in the study. Group 1 consisted of 14 subjects (mean age, 12.7 +/- 1.4 years) who were treated with RME, and Group 2 consisted of 13 subjects (mean age, 18.5 +/- 2.3 years) who were treated with SARME. In both groups, all cases had a maxillary width deficiency with bilateral crossbites. Maxillary dental casts were available at three different intervals: pretreatment (T1), after orthodontic treatment (T2), and at follow-up recall (T3). Intermolar and interpremolar width, palatal height, and maxillary arch depth and length were assessed from maxillary dental casts. Results: Treatment by RME and SARME produced significant increases in intermolar and interpremolar width and maxillary arch length after expansion (T2) (P < .05). The amount of relapse was not significantly different 2 years after treatment (P > .05). Conclusions: Although age ranges of the patient groups are different, the dentoalveolar responses of RME and SARME were similar after orthodontic treatment. (Angle Orthod. 2009:79;)