Background The residual SYNTAX score (RSS) quantitatively assesses angiographic completeness of revascularization after percutaneous coronary intervention (PCI). Objective The purpose of this study was to determine whether the RSS could predict one-year mortality more than Syntax score in patients with NSTE-ACS. Methods Patients admitted in our cardiology department between 01 November 2015 and 31 October 2016 for NSTE-ACS and treated by PCI were prospectively evaluated. The Syntax score and the residual syntax score (RSS) were calculated. The RSS was based on the recalculation of the SYNTAX score after PCI.A ROC curves were developed to define the SS and RSS score cutoffs that best predicts one-year mortality. Results Un total de 132 patients were evaluated: mean age was 62 ± 12 years and 66.7% were male. The one-year mortality was 3.8%. The syntax score and RS score in these patients were significantly higher (27.1 ± 6.5 vs. 15.8 ± 5.2; P = 0.005) and (22.4 ± 7.9 vs. 5.2 ± 6.5; P 22 showed a sensitivity of 80.0%, specificity of 81.6%. The area under the ROC curve was 0.85 (95% confidence interval of 0.74–0.96). Residual Syntax score > 18 showed a sensitivity of 80.0%, specificity of 96.4%. The area under the ROC curve was 0.95 (95% confidence interval of 0.88–1.00) ( Fig. 1 ). Conclusions We believe our results show that RSS more than SYNTAX score is a strong predictor of one-year mortality in patients with NSTEACS and that more extensive revascularization might improve the prognosis of these patients. However, randomized studies are needed to confirm this hypothesis.