Obstructive sleep apnea (OSA) is a commonly encountered problem in the perioperative setting even though many patients remain undiagnosed at the time of surgery. The objective of this systematic review was to evaluate whether the diagnosis of OSA has an impact on postoperative outcomes. We performed a systematic review of studies published in PubMed-MEDLINE, MEDLINE In-Process, and other nonindexed citations, Embase, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Health Technology Assessment up to November 2014. Studies of adult patients with a diagnosis of OSA or high risk thereof, published in the English language, undergoing surgery or procedures under anesthesia care, and reporting ≥1 postoperative outcome were included. Overall, the included studies reported on 413,304 OSA and 8,556,279 control patients. The majority reported worse outcomes for a number of events, including pulmonary and combined complications, among patients with OSA versus the reference group. The association between OSA and in-hospital mortality varied among studies; 9 studies showed no impact of OSA on mortality, 3 studies suggested a decrease in mortality, and 1 study reported increased mortality. In summary, the majority of studies suggest that the presence of OSA is associated with an increased risk of postoperative complications.