BACKGROUND: Rapid-eye-movement-sleep-dependent obstructive sleep apnea (REM-OSA) is a sleep breathing abnormality in which apneas/hypopneas occur mainly during REM sleep periods. However, the clinical significance of REM-OSA compared to sleep-stage-non-dependent OSA (SND-OSA) has been controversial. This study evaluated differences in the clinical features, polysomnography (PSG) characteristics, and subjective symptoms between REM-OSA and SND-OSA. METHODS: In total, 136 consecutive patients with mild-to-moderate OSA were enrolled. REM-OSA was defined as a rapid eye movement (REM):non-REM apnea-hypopnea index (AHI) ratio of >2 and a total duration of REM sleep exceeding 30 minutes. We compared the demographic, clinical, and PSG characteristics, and subject symptoms between REM-OSA and SND-OSA. RESULTS: The REM-OSA group comprised 45 (33%) of the 136 subjects. The mean age and total AHI did not differ between the groups, but there was a significant female predominance (35.6% vs. 16.5%) in the REM-OSA group. In terms of PSG parameters, subjects with REM-OSA showed a lower percentage of light sleep and a lower AHI in a supine position despite spending more sleep time in that position. Subjective sleep complaints, depression, anxiety, and health-related quality of life did not differ between the two study groups. CONCLUSIONS: The female predominance and sleep architecture differed between REM-OSA and SND-OSA in this study. The AHI in subjects with SND-OSA was dependent on sleep position rather than sleep stage. Further study is needed to elucidate the pathomechanism and clinical significance of REM-OSA.