A retrospective study of adults with Eisenmenger syndrome assessed at a tertiary referral center was performed to identify clinical characteristics and establish prognostic determinants. Mortality and cause of death are reported with baseline clinical data correlated with mortality to identify predictors of death. Clinical events during follow-up, including heart failure, atrial arrhythmia, hemoptysis, and syncope were also reviewed. A total of 109 adults with Eisenmenger syndrome (mean +/- SD age 29 +/- 11 years, 43% men) were followed for a median of 6.3 years. Sixty-six patients (61%) had simple cardiac anatomy (13 atrial septal defect, 43 ventricular septal defect, 10 patent ductus arteriosus). The remainder (43 patients) had complex cardiac anatomy (including atrioventricular septal defect, truncus arteriosus, univentricular heart, and transposition of the great arteries). There were 33 deaths and 9 transplantations during follow-up. Median survival was 53 years. Multivariate Cox regression analysis identified age at presentation (hazard ratio [HR] 0.90), supraventricular arrhythmia (HR 3.44), precordial electrocardiogram voltage (HR 1.61/mV increase), and poor New York Heart Association functional class (HR 2.60) as independent predictors of mortality. There is a large variation in the life expectancy for adults with Eisenmenger syndrome. Baseline characteristics associated with increased mortality include younger age at presentation (associated with complex anatomy), functional class, supraventricular arrhythmia, and an electrocardiogram index for right ventricular hypertrophy.