Introduction: Patients with Prader-Willi syndrome ( PWS) have been considered at high risk for obstructive sleep apnea (OSA) due to daytime sleepiness and high prevalence of morbid obesity. OSA has been suggested as a risk factor for sudden death in PWS patients treated with growth hormone (hGH) by promoting tonsillar growth and sleep surveillance is recommended. However, little is known regarding OSA and their management in pediatric PWS due to both availability and cost of polysomnograms ( PSGs). The aim of the study is to analyze PSG data in Korean patients with PWS and to investigate the impact of independent variables on OSA. Methods: PSG studies of pediatric patients with PWS performed in a single center between the years 2005-2017 were reviewed. Age, sex, body mass index (BMI) z-score, sleep indices including apnea-hypoapnea index (AHI), and therapies were analyzed. Results: Thirty PSG data from 30 PWS patients were analyzed. Median age was 7.8 years (0.5-19.6) and mean BMI was 1.7 ± 1.7. Of these 30 patients, 27 subjects had OSA, 5 subjects conducted adenotonsillectomy and 11 recommended positive airway pressure prescription (obese: 11, overweight:3, non-obese: 16). Among patients with OSA, 48.15% had mild OSA, 18.52% moderate OSA, and 33.33% severe OSA. Average hGH initiation age was 5.3 years. The mean AHI in our patients was 4.2 per hour (2.4-8.8) (normal 0-1 per hour). Of these, 3.0 per hour (1.2-8.1) were hypoapnea. By comparison between the two age groups (≥ 10 yr, 10 yr), gender, frequency, severity of OSA, genotype, and hGH treatment duration did not show statistical differences. Meanwhile, AHI and BMI were significantly higher in the age group 10 years and above compared to the group under the age of 10 years (AHI 19.4 vs 3.1 ( P=0.008); BMI 3.4 vs 0.9 ( P0.001)). Correlation analysis showed that AHI correlated positively with BMI (r = 0.464, P = 0.017), but did not correlate with age, and hGH treatment duration. Conclusions: In this study, pediatric patients with PWS showed a high AHI, mainly from hypoapnea index. HGH treatment had no significant correlation with an increase in AHI. Patients with PWS above 10 years old are at higher risk for OSA in relation to increasing obesity. Therefore, active intervention for obesity and early detection of OSA via regular sleep surveilance in all children with PWS are very important.