Maxillary expansion using either a quadhelix appliance (Qx) or a nickel titanium palatal expander (Nt) was prospectively compared in 28 consecutive new patients (19 female, nine male) presenting with posterior buccal segment crossbites. Study models taken at each activation were measured to determine the mean maxillary expansion efficacy (Emax) and the mean expansion rate (m(max)) across the first molars and first premolars. Patient discomfort was assessed using visual analogue scores, and cost-effectiveness was also considered. Neither Emax nor m(max) differed significantly between Qx and Nt across either the first molars or the first premolars. However, both Emax and m(max) were significantly greater across the first molars than across the first premolars only with Qx (Emax: 8.4 +/- 0.7 mm versus 5.1 +/- 0.6 mm, P = 0.001; m(max): 0.09 +/- 0.005 mm/day versus 0.05 +/- 0.006 mm/day, P = 0.0001). In addition, greater variance was apparent in m(max) with Nt than with Qx across both the first molars and the first premolars. Overall, Qx and Nt elicited similar discomfort. However, significantly less was reported with Nt on days 6 (P = 0.04) and 7 (P= 0.03) following the second 'activation'. These preliminary results suggest that Qx and Nt are equally efficacious maxillary expanders. However, Qx expansion appeared significantly more controlled, as well as more individually predictable in expansion rate. Overall, Qx and Nt probably elicit similar discomfort, but significantly less discomfort may be seen with Nt following the second activation. Finally, because more than one appliance is invariably required with Nt, Qx expansion is potentially less costly.