Background Adults with a systemic right ventricle (sRV) have a high risk of cardiac complications. This study aimed to identify prognostic markers in adults with sRV based on clinical evaluation, echocardiography, and blood biomarkers. Methods and Results In this prospective cohort study, consecutive clinically stable adults with sRV caused by Mustard- or congenitally corrected transposition of the great arteries were included (2011-2013). Eighty-six patients were included (age 37±9 years, 65% male, 83% New York Heart Association functional class I, 76% Mustard transposition of the great arteries, 24% congenitally corrected transposition of the great arteries). Venous blood sampling was performed including N-terminal pro B-type natriuretic peptide, high-sensitive-troponin-T, high-sensitivity C-reactive protein, growth differentiation factor-15, galectin-3, red cell distribution width, estimated glomerular filtration rate, and hemoglobin. Besides conventional echocardiographic measurements, longitudinal, circumferential, and radial strain were assessed using strain analysis. During a median follow-up of 5.9 (interquartile range 5.3-6.3) years, 19 (22%) patients died or had heart failure (primary end point) and 29 (34%) patients died or had arrhythmia (secondary end point). Univariable Cox regression analysis was performed using dichotomous or standardized continuous variables. New York Heart Association functional class >I, systolic blood pressure, and most blood biomarkers were associated with the primary and secondary end point (galectin-3 not for primary, N-terminal pro B-type natriuretic peptide and high-sensitivity C-reactive protein not for secondary end point). Growth differentiation factor-15 showed the strongest association with both end points (hazard ratios; 2.44 [95% CI 1.67-3.57, P<0.001], 2.00 [95% CI 1.46-2.73, P<0.001], respectively). End-diastolic basal dimension of the subpulmonary ventricle was associated with both end points (hazard ratio: 1.95 [95% CI 1.34-2.85], P<0.001, 1.70 [95% CI 1.21-2.38, P=0.002], respectively). Concerning strain analysis, only sRV septal strain was associated with the secondary end point (hazard ratio 0.58 [95% CI 0.39-0.86], P=0.006). Conclusions Clinical, conventional echocardiographic, and blood measurements are important markers for risk stratification in adults with a sRV. The value of novel echocardiographic strain analysis seems limited.