OBJECTIVES: This study evaluated the applicability of the German Registry of Acute Aortic Dissection Type A (GERAADA) score in predicting 30-day mortality in Japanese patients undergoing surgery for acute type A aortic dissection (ATAAD) and compared its predictive performance with that of the European System for Cardiac Operative Risk Evaluation II (EuroSCORE II). METHODS: This single-center retrospective study involved 154 patients who underwent emergency surgery for ATAAD between January 2019 and April 2024. The GERAADA and EuroSCORE II were calculated for each patient. Predictive accuracy for 30-day mortality was assessed using the area under the receiver operating characteristic curve (AUC). A multivariate logistic regression identified independent predictors of mortality, and long-term outcomes were evaluated using Kaplan-Meier analysis. RESULTS: The 30-day mortality rate was 11.0%. The GERAADA score showed an AUC of 0.80, indicating good discriminatory ability, while the EuroSCORE II demonstrated moderate performance with an AUC of 0.67 (P = 0.07). The GERAADA score significantly overestimated mortality in this cohort, whereas the EuroSCORE II underestimated it. Independent predictors of mortality included the use of catecholamines at referral. Kaplan-Meier analysis revealed a 1-year survival rate of 79.4% with an AUC of 0.72, demonstrating the GERAADA score's utility as a predictor of long-term survival. CONCLUSIONS: The GERAADA score provides accurate predictions of 30-day mortality in Japanese patients undergoing ATAAD surgery, comparable to the EuroSCORE II. This score demonstrates robust predictive ability for short- and long-term outcomes and may serve as a practical tool for risk stratification in ATAAD surgery.