The relative and combined effects of sleep apnea with diabetes mellitus (DM) on cardiovascular outcomes in patients undergoing coronary artery bypass grafting (CABG) remain unknown. In this secondary analysis of data from the SABOT study, 1007 patients were reclassified into four groups based on their sleep apnea and DM statuses, yielding 295, 218, 278, and 216 patients in the sleep apnea (+) DM (+), sleep apnea (+) DM (-), sleep apnea (-) DM (+), and sleep apnea (-) DM (-) groups, respectively. After a mean follow-up period of 2.1 years, the crude incidence of major adverse cardiac and cerebrovascular event was 18% in the sleep apnea (+) DM (+), 11% in the sleep apnea (+) DM (-), 13% in the sleep apnea (-) DM (+), and 5% in the sleep apnea (-) DM (-) groups. Using sleep apnea (-) DM (-) as the reference group, a Cox regression analysis indicated that sleep apnea (+) and DM (+) independently predicted MACCEs (adjusted hazard ratio, 3.2; 95% confidence interval, 1.7-6.2; p = 0.005) and hospitalization for heart failure (adjusted hazard ratio, 12.6; 95% confidence interval, 3.0-52.3; p < 0.001). Sleep apnea and DM have independent effects on the prognosis of patients undergoing CABG.Clinical trial registration: ClinicalTrials.gov identification no. NCT02701504.