BACKGROUND: Sleep-related breathing disorders(SRBD) and periodic leg movements disorder(PLMD) are both common, and are considered as separate sleep disorders. However, both disorders show high comorbidity. SRBD and PLMD can result in excessive daytime sleepiness and insomnia due to frequent sleep fragmentation So, it is very important to consider the presence of PLMD, when we are dealing with the diagnosis and management of SRBD. The objectives of this study were to determine the incidence of PLMD in patients with SRBD, and 13 describe any differences between patients with and without PLMD. METHOD: The authors reviewed the sleep recordings of 106 Patients with a final diagnosis of SRBD(obstruclive sleep apnea or upper airway resistance syndrome), who underwent full nocturnal polysomnography, including the monitoring of the anterior tibialis electromyogram. All sleep records were recorded and scored using the standard criteria. The data was analyzed by the student t-test. RESULT : 106 patients(M=76, F=30) were included in the analysis. Data revealed a mean age of 49.5 +/- 13.6 years, a respiratory disturbance index(RDI) of 22.3 +/- 25.4/hour sleep, a lowest oxygen saturation of 84.9 +/- 11.3%, a mammal esophageal pressure of -41.0 +/- 19.1cm H2O, and PLM index(PLMI) index(PLMI) 13.1 +/- 22.4 movements/ hour sleep. Forty four percent(47 of 106 patients) had a PLMI of greater than 5 on this study. The mean age of the patients with PLMD was significantly higher than that of the patients without PLMD(p < 0.005). Fe-male patients with SRBD accompanied more PLMD(p < 0.05). The apnea index of the patients with PLMD was significantly lower than that of the patients without PLMD(p < 0.01). The percentage of stage 1 sleep in the patients with PLMD was significantly lower than that of the patients without PLMD(p < 0.05). CONCLUSION: The prevalence of PLMD in the patients with SRBD was high at 44.3%. The patients with PLMD were older and had more high RDI in comparison to the patients without PLMD, which was consistent with previous findings. The authors recommend that more careful consideration of PLMD is required when diagnosing and treating SRBD.