This study compared the initial and long-term skeletal and dental effects of Herbst and Bass appliance therapy for correction of Class II malocclusion. The sample comprised 18 pairs of boys matched for growth period at the time of therapy, with similar pre-treatment sagittal and vertical jaw base relationships. One boy in each pair was treated with the Herbst and the other with the Bass appliance. At follow-up, 15 boys of the Herbst group and 17 of the Bass group were available. Lateral cephalograms in centric occlusion taken before treatment, after 6 months of treatment and at the end of growth were analysed. After 6 months of treatment the Bass appliance seemed to have a greater effect on mandibular jaw base position. The correction of overjet and sagittal molar relationship was more complete in the Herbst patients due to dental changes. At follow-up varying effects both between and within pairs were observed. Overall, the skeletal and dental changes from start of treatment to end of growth were of the same magnitude. A restraining effect on the position of the maxilla was observed in both groups, somewhat more pronounced in the Bass sample. Both treatment methods are most useful in correction of severe Class II malocclusions. It was, however, difficult to find possible differences in treatment effects between the two methods due to great individual variations of growth.