Purpose <p>Neuromuscular diseases (NMDs) are reported to have increased obstructive apnoea/hypopnoea during rapid eye movement (REM) sleep; however, the prevalence of REM-related obstructive sleep apnoea (OSA) and its clinical correlates in NMD remain undefined. We evaluated REM sleep, REM-related OSA frequency, and associated with demographic and clinical factors.</p> Methods <p>We retrospectively evaluated patients with NMDs who underwent polysomnography (PSG) between 2015 and 2024. Demographic data, morning arterial blood gases, spirometry and PSG data were collected. REM-related OSA required AHI ≥ 5 events/hour, REM-to-non-REM (NREM) AHI ≥ 2, and REM ≥ 30&#xa0;min; REM-isolated additionally required NREM AHI &lt; 5 events/hour. Patients with OSA who did not meet the criteria for REM-related OSA were classified as having NREM-related OSA.</p> Results <p>Among 290 patients, OSA was present in 87.6% (254/290). REM sleep duration was markedly reduced (11.8 ± 8.0%; 46.8 ± 32.2&#xa0;min), and 30.0% of patients had REM duration &lt; 30&#xa0;min. Among OSA with REM ≥ 30&#xa0;min (<i>n</i> = 182), 54.4% had REM-related OSA; 25.3% were REM-isolated. Compared with NREM-related OSA, the REM-related group exhibited more frequent female sex (<i>p</i> = 0.015), hypertension (<i>p</i> = 0.020), and depression (<i>p</i> = 0.025). In multivariable analysis, REM-related OSA was independently associated with morning hypercapnia (aOR 4.889; 95%CI 1.885–12.680), forced vital capacity (FVC) &lt; 50% and/or ≥ 20% upright-to-supine decline (aOR 3.847; 95%CI 1.085–13.642), and mild OSA (aOR 3.461; 95%CI 1.509–7.937).</p> Conclusions <p>Despite the marked reduction in REM sleep in NMDs, OSA, and particularly REM-related OSA, is common. In the REM-related OSA group, morning hypercapnia and FVC decline were more frequent. These observations suggest that REM-stage characteristics may be predictive of subsequent chronic respiratory failure.</p>