BACKGROUND: Among patients with obstructive sleep apnea (OSA) a higher number of medical morbidities are known to be associated with those that have obesity hypoventilation syndrome (OHS) compared to OSA alone. OHS can therefore pose a higher risk of postoperative complications after elective non-cardiac surgery (NCS) and is often unrecognized at the time of surgery. The objective of this study was to retrospectively identify patients with OHS and compare their postoperative outcomes with those who have OSA alone. METHODS: Patients meeting criteria for OHS were identified within a large cohort of patients with OSA who underwent elective NCS at a major tertiary care center. We identified postoperative outcomes associated with OSA and OHS as well as the clinical determinants of OHS (BMI, AHI). Multivariable logistic or linear regression models were used for dichotomous or continuous outcom...