Study Objectives: A previously published case report suggested that a chinstrap alone might improve obstructive sleep apnea (OSA). We conducted this study to determine whether a chinstrap was a feasible alternative to continuous positive airway pressure (CPAP) in patients with OSA.; Methods: 26 adult patients with OSA (apnea-hypopnea index [AHI] > 5/h on diagnostic polysomnogram [PSG]) underwent a modified split-night PSG, using only a chinstrap for the first 2 hours of sleep, followed by CPAP titration for the remainder of the night. Improvements in AHI, arterial oxygen saturation (SpO(2)), and snoring with chinstrap use were compared to results with optimal CPAP pressures.; Results: There was no significant difference between the diagnostic PSG and the chinstrap portion of the split-night PSG in the following parameters: general AHI (median [IQR] 16.0/h [9.7-26.0] vs. 25.9/h [10.7-42.7]), SpO(2) nadir (84.0% [80.5-87.5] vs. 87.0 [84.0-88.5]), AHI in REM sleep (26.7/h [16.8-43.7] vs. 42.4/h [21.3-57.7]), AHI in supine sleep (24.9/h [11.9-51.5] vs. 29.8/h [11.7-55.5]), snoring index (253.2/h [147.5-353.1] vs. 180.0/h [9.8-393.3]) or subjective snoring scale (3.0 [0.8-3.0] vs. 2.5 [0.4-3.0]). The AHI and SpO(2) nadir in the 13 patients with mild OSA also did not improve with chinstrap use (9.6/h [8.1-12.2] vs. 10.6/h [6.8-35.4] and 87.0% [83.0-90.0] vs. 88.0% [87.0-89.0]). All these parameters showed significant improvement with optimal CPAP titration (p < 0.05).; Conclusions: A chinstrap alone is not an effective treatment for OSA. It does not improve sleep disordered breathing, even in mild OSA, nor does it improve the AHI in REM sleep or supine sleep. It is also ineffective in improving snoring.