IMPORTANCE Angiotensin II is significantly associated with the pathogenesis of acute aortic dissection. Angiotensin II type 1 receptor agonistic autoantibodies (AT1-AAs) can mimic the effect of angiotensin II. OBJECTIVE To investigate the association between AT1-AAs and all-cause and cause-specific mortality risk in patients with acute aortic dissection. DESIGN, SETTING, AND PARTICIPANTS A total of 662 patients with clinically suspected aortic dissection from 3 medical centers inWuhan, China, were enrolled in this cohort study from August 1, 2014, to July 31, 2016. Of these, 315 patients were included in the 3-year follow-up study. Follow-up was mainly performed via telephone interviews and outpatient clinic visits. Data analysis was conducted from March 1 toMay 31, 2020. MAIN OUTCOMES AND MEASURES The primary outcomes of interest were all-cause mortality, death due to aortic dissection, and late aortic-related adverse events. RESULTS The full study cohort included 315 patients with AAD (mean [SD] age, 56.2 [12.7] years; 230 men [73.0%]). Ninety-two patients (29.2%) were positive for AT1-AAs. The mortality of AT1-AA-positive patients was significantly higher than that of AT1-AA-negative patients (40 [43.5%] vs 37 [16.6%]; P <.001). The mortality risk in AT1-AA-positive patients was always significantly higher than that in AT1-AA-negative patients in patients with both type A and type B dissection. Multivariable analysis showed that the risk of AT1-AA-positive patients for type A dissection was significantly higher than that of AT1-AA-negative patients (odds ratio [OR], 1.88; 95% CI, 1.12-3.13; P =.02). The Cox proportional hazards regression model showed a significant increase of all-cause mortality risk (OR, 2.27; 95% CI, 1.44-3.57; P <.001) and late aortic-related adverse events (OR, 1.58; 95% CI, 1.062.36; P =.03) among AT1-AA-positive patients during the follow-up period compared with AT1-AA-negative patients. CONCLUSIONS AND RELEVANCE This cohort study first detected AT1-AAs in patients with acute aortic dissection. The presence of AT1-AAs was associated with significantly higher all-cause and cause-specific mortality during a follow-up period of 3 years. The antibodiesmay be a risk factor for aortic dissection.