Study objective: To determine the association between postoperative complications and a high versus low risk of obstructive sleep apnea (OSA) as determined via screening tools. Design: Systematic review and meta-analysis of cohort studies. PubMed, EMBASE, Web of Science, and the Cochrane Library were searched from their inception to January 5, 2021. Setting: Operating room, postoperative recovery area, and ward. Patients: Adult patients scheduled for surgery. Interventions: We used Review Manager 5.4 to pool the data. The quality of evidence was rated using the Grading of Recommendations, Assessment, Development and Evaluation system. Measurements: The primary outcome was the composite endpoint of postoperative respiratory complications. The secondary outcomes were postoperative cardiac and neurological complications, intensive care unit (ICU) admission, and mortality. Main results: Twenty-six studies with 50,592 patients were included. A STOP-Bang score > 3 (versus <3) was associated with higher incidences of postoperative respiratory (odds ratio [OR], 2.11; 95% confidence interval [CI], 1.66-2.68) and neurological complications (OR, 3.60; 95% CI, 1.56-8.31). A STOP-Bang score > 5 (versus <5) was associated with higher incidences of postoperative respiratory (OR, 2.37; 95% CI, 1.11-5.04) and cardiac complications (OR, 4.95; 95% CI, 1.22-20.00) and higher in-hospital mortality (OR, 26.39; 95% CI, 2.89-241.30). A Berlin score > 2 (versus <2) was not associated with the incidence of postoperative complications, ICU admission, or mortality. The quality of evidence for all outcomes was very low. Conclusions: Very low-quality evidence suggested that a high risk of OSA, as assessed using the STOP-Bang questionnaire, was associated with a higher incidence of postoperative respiratory complications, and may also be associated with higher incidences of postoperative cardiac and neurological complications than a low risk of OSA. Since most of the included studies did not adjust for confounding factors, our findings need to be interpreted with caution. PROSPERO registration number: CRD42021220236.