Abstract Background Genetic aortopathy (GA) underlies thoracic aortic aneurysms (TAA) in younger adults. Comparative survival and predictors of outcomes in nonsyndromic TAA (NS-TAA) are incompletely defined compared to Marfan syndrome (MFS) and bicuspid aortic valve (BAV). Objectives The study sought to compare survival and clinical outcomes for individuals with NS-TAA, MFS, and BAV. Methods From 1988 to 2014, all patients presenting with GA 16 to 60 years of age were enrolled in a prospective study of clinical outcomes. Risk factors for death and aortic dissection were identified by Cox proportional hazards modeling and a mortality risk score developed. Results Diagnosis of GA was made for 760 patients (age 36.9 ± 13.6 years, 26.8% female; NS-TAA, n = 311; MFS, n = 221; BAV, n = 228). MFS patients were younger than NS-TAA and BAV. Presentation with aortic dissection was more common for NS-TAA than MFS or BAV. The 687 patients surviving >30 days after presentation were followed for a median of 7 years. Calculated 10-year mortality was 7.8% for NS-TAA, 8.7% for MFS, and 3.5% for BAV (NS-TAA and MFS vs. BAV p <0.05). Factors associated with all-cause mortality were MFS (p = 0.04), age at presentation, and family history of dissection. Conclusions Clinical outcomes for MFS and NS-TAA are similar but worse than BAV. Independent predictors of mortality, including family history of aortic dissection and age, can be included in an Aortopathy Mortality Risk Score to predict survival. Management of NS-TAA, including surgical intervention, should be similar to that of MFS.