Background: Readmissions after cardiac surgery are a relevant issue both for patients and the health care system in general. There are limited data about the relationship between readmissions after cardiac surgery and patient prognosis, or their impact on longterm mortality. Objective: The aim of this study was to analyze the incidence and the predictive factors of 30-day readmissions after cardiac surgery and their association with long-term mortality. Methods: The Division of Cardiac Surgery computerized database was retrospectively analyzed. The analysis included all consecutive patients undergoing cardiac surgery, discharged during the period between June 2010 and May 2013. Patients undergoing heart transplantation were excluded from the study. Readmission was defined as unplanned hospital admission within 30 days following discharge. Cardiovascular or non-cardiovascular death 30 days after discharge and until the end of follow-up period was considered as long-term mortality. Results: A total of 1,327 patients were included in the study and 184 (13.9%) were readmitted to hospital. Median follow-up was 826 days (IQR 581 to 1,085 days). Readmitted patients presented higher rate of comorbidities, as chronic obstructive pulmonary disease (6.5% vs. 2.1%; p=0.002) and heart failure (12% vs. 6%; p=0.0064). Also, in this group there was greater incidence of postoperative complications, as atrial fibrillation (35% vs. 19%; p <0.0001) and low cardiac output (9.2% vs. 4%; p=0.004). Infections (not mediastinitis) (25%), arrhythmias and permanent pacemaker implantation (15.2%), heart failure (13%), pleural effusion (6.5%), pericardial effusion (3.8%), fever of unknown origin (3.26%) and mediastinitis (6%), among others, were the most frequent causes of readmission. Logistic regression analysis showed that the factors associated with greater risk of readmission were cardiac surgery not involving coronary artery bypass grafting (OR 2.29; 95% CI 1.55-3.37; p <0.0001), history of pulmonary disease (OR: 2.95; 95% CI 1.32-6.6; p=0.0084), atrial fibrillation (OR 1.99; 95% CI 1.34-2.94; p=0.0005) and body mass index (OR 1.046; 95% CI 1.008-1.085; p=0.017). Considering the primary endpoint, readmissions were significantly associated with increased mortality at 1 and 3 years: 8.7% vs. 2.3%; p <0.0001 and 13.6% vs. 4.2%; p <0.0001, respectively. Conclusions: Readmission within 30 days after cardiac surgery is significantly associated with long-term mortality. The implementation of adequate care measures could reduce the probability of readmissions and, hence, improve the prognosis of this group of patients.