Primary Objective: To determine whether, in obese children with moderate-severe OSA who are prescribed PAP therapy, increased hours of PAP usage per night over a one-year period is associated with a greater improvement in HOMA-IR. Secondary Objectives: To determine whether increased hours of PAP usage per night is associated with a greater improvement in the following outcomes: 1) sympathetic nervous system activation (systolic and diastolic hypertension, nocturnal hypertension, heart rate and heart rate variability); 2) inflammation 3) neurobehavioral and quality of life measures. Methods: Study design: prospective multi-centre cohort study. Study Population: Obese children (body mass index (BMI) ≥ 95th %ile for age and sex) 8-17 years old with moderate-severe OSA will be recruited for this study from four pediatric tertiary care centres across Canada. As per current standard of care, those children with moderate-severe OSA, defined as ≥ 10 obstructive events per hour on polysomnography, will be prescribed PAP treatment. Sample Size: We expect a medium effect size (0.5); therefore 10 subjects per parameter tested (n=4) in the regression model and 25% attrition requires the recruitment of 54 subjects. Measurements will be made at baseline and 12 months. Data collection will include HOMA-IR, 24-hr blood pressure measurements, electrocardiogram for heart rate and heart rate variability, C-reactive protein as a marker of inflammation, neurobehavioral/quality of life measures (Conners parent and teacher scales, Child Behavior Checklist and Pediatric Quality of Life Inventory) and physical activity questionnaire (Habitual Activity Estimation Scale (HAES)). Data Analysis: Multivariate linear regression analyses will be performed for our primary and secondary outcomes. Our dependent variable will be change in HOMA-IR; our primary independent variable will be average number of hours/night of PAP usage. Adjustment variables will be change in BMI %ile, pubertal stage (Tanner stage 1-2 vs.