The residual SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) score (RSS) quantitatively assesses angiographic completeness of revascularization after percutaneous coronary intervention (PCI) and has been shown to be a predictor of events after angiography-guided PCI. In stable patients undergoing functionally complete revascularization with fractional flow reserve (FFR) guidance, RSS did not predict outcome. Whether this is also true in patients with acute coronary syndromes (ACS) is unknown.The purpose of this study was to determine whether the RSS could predict outcomes in patients with ACS.From the DANAMI-3-PRIMULTI (Primary PCI in Patients With ST-elevation Myocardial Infarction and Multivessel Disease: Treatment of Culprit Lesion Only or Complete Revascularization), FAME (Fractional Flow Reserve Versus Angiography for Multivessel Evaluation), and FAMOUS-NSTEMI (Fractional Flow Reserve Versus Angiographically Guided Management to Optimise Outcomes in Unstable Coronary Syndromes) trials, 547 patients presented with ACS and underwent functionally complete revascularization. Major adverse cardiac events (MACE) were defined as the composite endpoint of all-cause death, nonfatal myocardial infarction, and any repeat revascularization. The RSS was based on the recalculation of the SYNTAX score after PCI. We compared differences in 2-year outcome by the RSS subgroups: 0, 1 to <5, 5 to <10, ≥10 (RSS = 0 represents angiographically complete revascularization).The study population consisted of 271 patients with unstable angina/non-ST-segment elevation myocardial infarction and 276 with ST-segment elevation myocardial infarction. The mean RSS was 6.7 ± 5.8. MACE at 2 years occurred in 69 patients (12.6%). Patients with and without MACE had similar RSS after PCI (RSS: 7.2 ± 5.5 vs. 6.6 ± 5.9; p = 0.23). Kaplan-Meier curve analysis showed a similar incidence of MACE regardless of the RSS subgroups (p = 0.54). With and without adjustment of clinical variables, RSS was not a significant predictor of MACE or of each component of MACE.After complete revascularization of functionally significant stenosis by FFR, the extent of residual angiographic disease is not associated with subsequent ischemic events in patients presenting with ACS. These results suggest that the concept of functionally complete revascularization is applicable even in ACS patients. (Fractional Flow Reserve Versus Angiography for Multivessel Evaluation [F.A.M.E.] NCT00267774; Fractional Flow Reserve Versus Angiographically Guided Management to Optimise Outcomes in Unstable Coronary Syndromes [FAMOUS NSTEMI] NCT01764334; Primary PCI in Patients With ST-elevation Myocardial Infarction and Multivessel Disease: Treatment of Culprit Lesion Only or Complete Revascularization [DANAMI-3-PRIMULTI]; NCT01960933).