Abstract Background There is a paucity of evidence on the combination of the SYNTAX score II (SSII) and erythrocyte sedimentation rate (ESR) in assessing the long-term prognosis of patients with ST-elevated myocardial infarction (STEMI) and multivessel disease. The objective of this study was to investigate whether the ESR could enhance the predictive value of SSII on the long-term prognosis of STEMI patients. Methods A retrospective cohort study involving 483 STEMI and multivessel disease subjects receiving primary percutaneous coronary intervention was conducted. Major adverse cardiovascular events (MACE) included cardiovascular death, acute heart failure, recurrent myocardial infarction, revascularization, and nonfatal stroke. The predicted values of different models were estimated by a likelihood ratio test, Akaike’s information criteria (AIC), receiver operating characteristic (ROC) curves, net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Results During the follow-up period of up to 52 months, both the SSII and ESR were independently associated with MACE (hazard ratio [HR] = 1.032, p