ObjectivesTo explore the predictive value of platelet count at admission for long-term prognosis in patients with type B acute aortic dissection (AAD) undergoing endovascular therapy (EVT). MethodsWe investigated 131 consecutive patients with type B AAD after EVT in West China Hospital of Sichuan University from January to December 2012. The patients’ basic clinical data, blood test results, major adverse cardiovascular events, and in-hospital and out-hospital survival status were collected. According to the tri-sectional quantiles of platelet counts, the patients were divided into three groups. Chi-square test was used to analyze the correlation between platelet count and hospital complications. Kaplan-Meier survival analysis and Cox regression analysis were used to analyze the relationship between platelet count and survival in patients with type B AAD. The primary endpoint was all-cause death. ResultsThe overall in-hospital mortality of the 131 patients was 9.9%, and the mortality was 16.0% by the end of the follow-up, the median length of which was 2.1 years. There were 44 cases in T1 group (platelet count >200×10 9/L), 44 cases in T2 group [platelet count (155–200)×109/L], and 43 cases in T3 group [platelet count ≤155×109/L]. The mortality in T3 group (30.2%) was higher than that in T1 group (4.5%) and T2 group (13.6%) (P=0.004). Kaplan-Meier survival analysis showed that the cumulative survival rate of T3 group was significantly lower than that of T1 group and T2 group (69.8% vs. 95.5%, χ2=10.165, P=0.001; 69.8% vs. 86.4%, χ2=5.174, P=0.037). Cox multivariate analysis showed that age [hazard ratio (HR)=1.043, 95% confidence interval (CI) (1.009, 1.079), P=0.013], heart rate [HR=1.030, 95%CI (1.004, 1.058), P=0.024], and platelet count [HR=6.011, 95%CI (1.319, 27.391), P=0.020] were independent risk factors for mortality. Older age, rapid heart rate, and lower platelet count would increase the risk of death. ConclusionPlatelet count may be an independent factor that affects the prognosis of patients with type B AAD after EVT, and a low platelet count at admission increases the risk of death.