OBJECTIVE To evaluate the transverse dimensions of the maxillary arch induced by fixed self-ligating and traditional straight-wire appliances during orthodontic therapy. METHODS Forty consecutive patients (age range 14 to 30 years) with normal or low mandibular plane angle, normal overbite, and mild crowding were included. The traditional appliance was composed of Victory Series MBT brackets (3M Unitek), and the self-ligating appliance of Damon-3MX brackets (Ormco). The leveling and aligning phase with round archwires lasted 6 months and was followed by another 6 months of rectangular archwires. The archwire sequence with the MBT appliance was 0.016-inch and 0.019 3 0.025-inch Ni-Ti form II (3M Unitek), while in the Damon-3MX, it was 0.014-inch and 0.016-inch followed by 0.016 3 0.025-inch copper nickel-titanium (Ormco). Intercanine, first and second interpremolar, and intermolar widths in the maxilla were recorded before treatment (T0) and 12 months later (T1). RESULTS In both groups, a significant increase from T0 to T1 was recorded for all transverse measurements, but no significant difference was observed between groups. CONCLUSIONS Within 12 months of treatment, both appliances increased maxillary dentoalveolar widths.