Objective: To broaden the data supporting the use of the residual SYNTAX score (rSS) to define "reasonable" incomplete coronary revascularization (ICR) in order to improve the allocation of patients with severe coronary artery disease (CAD) to surgical/percutaneous revascularization and long-term clinical outcomes. Introduction: ICR is associated with a worse prognosis in patients with severe CAD, yet no consensus exists regarding its definition. Methods: We studied 148 consecutive patients with triple vessel/left main (3VD/LM) CVD treated by percutaneous coronary interventions (PCI). Clinical outcomes at 3 years were collected; the SS and rSS were calculated. We used various definitions of "reasonable" ICR:no post-PCI total occlusion, single vs. mutivessel residual post-PCI disease, and the rSS at a cutoff value determined according to ROC curve fitted for 3 years major adverse cardiovascular and cerebrovascular adverse events (MACCE) in order to determine which definition has the strongest correlation with long-term outcomes. Results: rSS 8 was associated with significant reductions in 3 year MACCE (19.4 vs. 51.1%, HR 5 3.62, P 5 0.014) Death/MI/ CVA (13.7 vs. 28.8%, HR 5 6.01, P 5 0.030) and repeat revascularization (8.6 vs. 28.9%, HR 5 3.44, P 5 0.033) using a Cox proportional hazard ratio model adjusted to baseline characteristics, whereas single vessel residual disease and absence of total occlusion were not. Conclusions: "Reasonable" ICR as determined by rSS carries better long-term prognosis in terms of clinical outcomes vs. more extensive residual coronary disease in patients with 3VD/LM coronary artery disease treated by PCI. The rSS may improve the allocation of coronary patients to the optimal mode of revascularization. V C 2015 Wiley Periodicals, Inc.