Cephalometric radiographs were taken before and after treatment in three groups of patients. Ten were treated with removable appliance therapy involving extraction of upper first premolars and retraction of anterior teeth. Ten were treated on a non extraction basis coupled with wearing an upper expansion appliance followed by an Andresen appliance. Another group of ten patients were treated in an identical manner except that they wore a Twin Block instead of the Andresen appliance. When comparing the patient groups before and after treatment, statistically significant differences were found for upper incisor angulation in the Removable (t = 9.49 p < 0.001) Andresen (t = 4.48 p < 0.001) Twin Block (t = 2.81 p < 0.001) groups and for angle ANB in the Andresen (t = 2.88 p < 0.01) and Twin Block (t = 2.65 p < 0.01) groups. Thus the overjet was reduced purely by incisor tipping with the removable appliance as would be expected, but both functional appliances produced some bodily correction with an improvement in the dental base relationship. Although the Twin Block appliance group showed a greater reduction in angle ANB this was not significantly different from that in the Andresen appliance group. The treatment time from insertion of the first appliance to reduction of the overjet to 3mm or less was also recorded. The treatment time for the Twin Block group (8.1 months) was significantly less (t = 2.79 p < 0.05) than the Andresen group (12.8 months), but neither functional group differed significantly from the removable appliance group (10.1 months).