Background Procalcitonin (PCT) is an acute phase protein which plasma levels raise also in sterile inflammation. For this reason, its role in the acute coronary syndrome (ACS) setting would be twofold: as a marker of infection and also as a prognosticator of generic inflammation. High PCT values have been related to worse prognosis in patients with cardiogenic shock. If PCT values may predict the risk of bacterial infections and long–term outcome in patients with acute coronary syndromes has been less investigated. Methods Consecutive patients with a diagnosis of ACS with PCT level assessed during the first 24 hours of hospitalization were enrolled. The primary outcome was the occurrence of bacterial infection defined by the occurrence of fever and of at least one positive blood or urinary culture with clinical signs of infection. The secondary outcome was the 1–year occurrence of the composite outcome all–cause mortality, stroke and myocardial infarction. Results Overall 569 patients have been enrolled (mean age 69.37±14 years, 30% females): 44 (8%) of them met criteria for bacterial infection. Age, female sex, smoking habit, heart rate, systolic blood pressure (SBP), heart failure after admission, coronary angiography, hemoglobin, creatinine clearance and PCT above the cut–off value were predictors of the outcome. After multivariate analysis, PCT and SBP resulted as independent predictors of bacterial infections (OR for PCT above the cut–off 2.67, 95%CI 1.09–6.53, p = 0.032; OR for SBP 0.98, 95%CI 0.97–0.99, p = 0.043). At 1–year, the composite outcome of all–cause death, MI and stroke occurred in 104 patients (18%). PCT did not result as an independent predictor of the composite outcome. Conclusions In patients with ACS PCT levels at hospital admission are predictor of bacterial infection but not of the composite lomg–term outcome of all–cause mortality, stroke and myocardial infarction.