Objective To evaluate the severity of the dental arch relationships and the treatment outcomes of reverse headgear (RHG) in southern Chinese patients with unilateral cleft lip and palate (UCLP). Design A retrospective study. Setting Faculty of Dentistry, The University of Hong Kong. Patients Thirty-eight UCLP patients with complete records. Among them, 14 were later treated with RHG (RHG group) and 24 were under review (non-RHG group) before definitive orthodontic or in conjunction with orthognathic surgery. Interventions Study models at T1 (aged 9.4 ± 0.4 years old), prebone grafting and before any orthodontic treatment started; T2 (aged 11.3 ± 0.6 years old), after bone grafting, and RHG treatment (RHG group) or under review (non-RHG group); and T3 (aged 15.3 ± 3.2 years old), pretreatment of definitive orthodontic or in conjunction with orthognathic surgery. Main Outcome Measures With satisfactory intra- and interexaminer agreement proven by the kappa value, the dental arch relationships of the study models at T1, T2, and T3 were assessed by a solo calibrated examiner using the GOSLON Yardstick. Results The median GOSLON score for southern Chinese patients with UCLP at T1 was 4.0. Sixty percent of the patients were categorized as "poor" at T1. RHG significantly improved dental arch relationships from T1 to T2, and the improvement was maintained until T3 assessed by the GOSLON Yardstick. Conclusions The dental arch relationships in southern Chinese UCLP patients at 8 to 10 years old are unfavorable. RHG treatment shows positive effects in improving the dental arch relationships in UCLP patients, as assessed by the GOSLON Yardstick.