ObjectiveCell division cycle 42 (CDC42) regulates CD4+T-cell differentiation and participates in vascular stiffness and atherosclerosis and is involved in the progression of Stanford type B aortic dissection (TBAD). This study aimed to explore the correlation between serum CDC42 level and CD4+T cell subsets and in-hospital mortality in TBAD patients.MethodsSerum CDC42 and peripheral blood T-helper (Th) 1, Th2, and Th17 cells were detected in 127 TBAD patients by enzyme-linked immunosorbent assay and flow cytometry, respectively. Serum CDC42 was also quantified in 30 healthy controls.ResultsSerum CDC42 was decreased in TBAD patients vs. healthy controls (median [interquartile range (IQR)]: 418.0 (228.0–761.0) pg/ml vs. 992.0 (716.3–1,445.8) pg/ml, P