Purpose: The purpose of this study was to evaluate whether maximum forced inspiratory airflow changes occur by changing the jaw position in Japanese normal subjects and patients with obstructive sleep apnea (OSA) classified by their craniofacial features. Materials and Methods: The subjects included 8 male non-OSA subjects and 15 male patients with OSA whose conditions had been diagnosed with a polysomnographic recording. The OSA subjects were divided into 2 groups by means of a craniofacial (CF) score based on cephalometric variables: a high-score group (CF score >= 4) and a low-score group (CF score £ 3). A case-control design was utilized to assess group differences (control and 2 patient groups). Airflow changes were determined using a spirometer that assessed the velocity of airflow during forced inspiration. Maximum forced inspiratory airflow was measured in 4 positions in all patients. Results: All 3 groups had a significant decrease in their maximum forced inspiratory airflow upon reclining, and there were no significant group differences regarding the magnitude of this change. The OSA subjects returned to baseline measurements more than controls when the jaw was positioned forward, as the jaw was progressively advanced in high CF score subjects. Conclusion: This study suggested that a protrusive jaw position allows more inspiratory airflow to occur in OSA patients compared to controls, and this was significant in the patients with a high CF score.