This study investigates the causal relationship between immune cells and generalized anxiety disorder (GAD) using Mendelian randomization (MR). The researchers analyzed data from the FinnGen dataset, which included 4,666 cases and 337,577 controls, and 731 immune cell traits derived from the GWAS catalog. Both forward and reverse MR analyses were conducted to explore the causal effects of immune cell traits on GAD and vice versa. After adjusting for false discovery rate (FDR), GAD did not show a statistically significant effect on immunophenotypes. However, several phenotypes, such as decreased PB/PC levels in B cells, reduced PB/PC AC in GAD patients, and diminished PB/PC on lymphocytes, were noted. GAD also had a causal effect on CD27 on IgD-CD38br, CD20-% cell, IgD-CD38br% lymphocyte, FSC-A level on granulocytes, and CD4RA on TD CD4+. Additionally, two lymphocyte subsets, CD24+ CD27+ B cells and CD28+CD4+ T cells, were identified as significantly associated with GAD risk. The study concludes that there is a close association between immune cells and GAD, providing insights for future clinical research.This study investigates the causal relationship between immune cells and generalized anxiety disorder (GAD) using Mendelian randomization (MR). The researchers analyzed data from the FinnGen dataset, which included 4,666 cases and 337,577 controls, and 731 immune cell traits derived from the GWAS catalog. Both forward and reverse MR analyses were conducted to explore the causal effects of immune cell traits on GAD and vice versa. After adjusting for false discovery rate (FDR), GAD did not show a statistically significant effect on immunophenotypes. However, several phenotypes, such as decreased PB/PC levels in B cells, reduced PB/PC AC in GAD patients, and diminished PB/PC on lymphocytes, were noted. GAD also had a causal effect on CD27 on IgD-CD38br, CD20-% cell, IgD-CD38br% lymphocyte, FSC-A level on granulocytes, and CD4RA on TD CD4+. Additionally, two lymphocyte subsets, CD24+ CD27+ B cells and CD28+CD4+ T cells, were identified as significantly associated with GAD risk. The study concludes that there is a close association between immune cells and GAD, providing insights for future clinical research.