Objectives <p>Herbst appliance treatment results in posterior airway space (PAS) increase. The published data, however, is based on rather small samples and shows large inter-individual variation. Therefore, the current aim was to investigate PAS changes during and after Herbst plus subsequent multibracket appliance (MBA) treatment in a retrospective cohort study and to search for possible pre-treatment influencing factors.</p> Materials and methods <p>503 former Class II:1 patients (overjet = 7.8 ± 2.4&#xa0;mm, ANB angle = 5.0 ± 2.1°) who had undergone treatment at 13.8 ± 3.4 years (Department for Orthodontics, University of Giessen, Germany). Cephalograms from before (T0), after 24.9 ± 9.2 months of treatment (T1) and 26.1 ± 8.0 months after treatment (T2) were analysed for PAS changes (area-size and linear distances p, t, pC2, pC3, pC4. In addition, possible influencing pre-treatment characteristics were evaluated: overjet, ANB angle, Wits appraisal, ML/NSL angle, ArGoGn angle, age and skeletal maturity.</p> Results <p>On average, the PAS area increased by 23% during Herbst-MBA treatment (T1-T0) and remained constant (± 0%) thereafter (T2-T1). All linear distances also increased (6–19%) during T1-T0 and showed further increase (1–7%) during T2-T1. For all variables a large inter-individual variation existed. With regard to possible influencing factors on PAS changes, significant associations were observed for pre-treatment age and Wits appraisal of the patients.</p> Conclusions <p>PAS increases during Herbst-MBA treatment. For none of the assessed variables, relapse occurred afterwards. Young age and a large Wits appraisal were determined to be beneficial for PAS enlargement.</p> Clinical relevance <p>Herbst-MBA treatment seems to have a positive effect in the majority of Class II patients with reduced PAS.</p>