Study Objectives: To explore differences in craniofacial structures and obesity between Caucasian and Chinese patients with obstructive sleep apnea (OSA). Design: Inter-ethnic comparison study. Setting: Two sleep disorder clinics in Australia and Hong Kong. Patients: 150 patients with OSA (74 Caucasian, 76 Chinese). Interventions: Anthropometry, cephalometry, and polysomnography were performed and compared. Subgroup analyses after matching for: (1) body mass index (BMI); (2) OSA severity. Measurements and Results: The mean age and BMI were similar between the ethnic groups. Chinese patients had more severe OSA (AHI 35.3 vs 25.2 events/h, P = 0.005). They also had more craniofacial bony restriction, including a shorter cranial base (63.6 ± 3.3 vs 77.5 ± 6.7 mm, P < 0.001), maxilla (50.7 ± 3.7 vs 58.8 ± 4.3 mm, P < 0.001) and mandible length (65.4 ± 4.2 vs 77.9 ± 9.4 mm, P < 0.001). These findings remained after correction for differences in body height. Similar results were shown in the BMI-matched analysis (n = 66). When matched for OSA severity (n = 52), Chinese patients had more craniofacial bony restriction, but Caucasian patients were more overweight (BMI 30.7 vs 28.4 kg/m2, P = 0.03) and had a larger neck circumference (40.8 vs 39.1 cm, P = 0.004); however, the ratios of BMI to the mandible or maxilla size were similar. Conclusions: Craniofacial factors and obesity contribute differentially to OSA in Caucasian and Chinese patients. For the same degree of OSA severity, Caucasians were more overweight, whereas Chinese exhibited more craniofacial bony restriction.