Aims: The SYNTAX score has been proposed as a valuable tool to characterise coronary anatomy prospectively based on its complexity. This study evaluated the prognostic value on adverse outcomes of the residual SYNTAX score (rSS) in patients with complex lesions treated with an everolimus-eluting stent (EES). Methods and results: One thousand eight hundred and fifty-one patients with small vessel (reference diameter <2.75 mm), long lesion (length >25 mm), or multivessel (>2 target vessels) disease who underwent percutaneous coronary intervention (PCI) with EES in the prospective SEEDS (A Registry To Evaluate Safety And Effectiveness Of Everolimus Drug Eluting Stent For Coronary Revascularization) trial were categorised into low (<6), mid (>6-<12) and high (>12) baseline SYNTAX score (bSS) groups, and into low (=0), mid (>0-<5) and high (>5) rSS groups. Mean bSS and rSS were 10.87 +/- 7.26 and 2.18 +/- 3.97, respectively; 64% of patients had complete revascularisation (rSS=0). At 12 months the primary outcome of ischaemia-driven target vessel failure (TVF, composite of cardiac death, target vessel myocardial infarction and ischaemia-driven target vessel revascularisation) was significantly higher in the high bSS and rSS groups than in the respective lower groups (p<0.01 for both). In multivariable analysis, rSS was an independent predictor of TVF (hazard ratio: 1.403, 95% confidence interval: 1.081 to 1.820, p=0.01). Conclusions: Twelve-month TVF was significantly higher in the highest rSS group; rSS with a cut-off of 5 might therefore allow the risk stratification of patients with complex lesions treated with a second-generation drug-eluting stent (ClinicalTrials.gov identifier: NCT 01157455).