Obstructive sleep apnea (OSA) is growing in prevalence though it still remains significantly underdiagnosed. Preoperative screening for OSA is taking place in many institutions, with a substantial number of patients being identified as having a high probability for OSA just prior to undergoing surgery. Emerging data increasingly demonstrates that patients with a high probability of having OSA as well as those with a known diagnosis of OSA may be at increased risk for developing complications in the perioperative setting. Postoperative cardiac and pulmonary adverse events appear to occur more frequently in these patients though the impact OSA has on postoperative mortality is controversial. In addition, determining which patients are at greatest risk remains an area of uncertainty. This chapter will review the current state of the knowledge regarding OSA as a risk factor for perioperative complications.