The fibrinogen-to-albumin ratio index (FAR) is a valuable tool reflecting the systemic inflammation level and associated with the severity of coronary artery disease. However, the utility of the FAR in predicting the long-term prognosis of patients with ST-elevation myocardial infarction (STEMI) and multivessel disease has remained to be determined. A total of 424 patients diagnosed with STEMI and multivessel disease were recruited for the present study. They were given emergent percutaneous coronary intervention treatment and then completed a follow-up for primary (all-cause mortality) and secondary endpoints (major adverse cardiac events, including MI, stroke, emergent revascularization and rehospitalization due to heart failure). The association between FAR and the Synergy Between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) score was investigated, while receiver operating characteristic curve analysis was adopted to assess the ability of the FAR to predict long-term outcomes. The long-term survival of high and low FAR groups was compared by drawing Kaplan-Meier survival curves. Multivariate Cox regression analysis was adopted to evaluate the risk factors of primary and secondary endpoints. The FAR was revealed to have a linear correlation with the SYNTAX score (y=0.022x+17.737; P=0.015). Furthermore, the FAR was a significant predictor of all-cause death with a cutoff value of 128.4 (area under the curve, 0.832; P<0.001). A significant difference was determined between the high FAR group and the low FAR group in terms of the proportion of patients with the primary endpoint (P<0.001) and secondary endpoint (P=0.001). It was demonstrated that the FAR was an independent risk factor for all-cause death of patients with STEMI and multivessel disease (hazard ratio, 1.029; 95% CI: 1.020-1.037; P<0.001). In summary, the FAR is a valuable biomarker associated with STEMI and may be useful in the prediction of the long-term prognosis of patients with STEMI and multivessel disease.