<h4>Introduction</h4>To investigate the relationship between CD4(+)CD25(+)CD127(dim) regulatory T cells (Tregs) and immune imbalance in acquired severe aplastic anemia (SAA).<h4>Methods</h4>The quantity of CD4(+)CD25(+)CD127(dim) Tregs in 44 SAA patients and 23 normal controls were measured by flow cytometry. The gene discussed is CD4; the disease is severe aplastic anemia.