Systemic lupus erythematosus (SLE) is an autoimmune disease with a complex multifactorial pathogenesis. T lymphocytes play a critical role in disease pathogenesis and display abnormal gene expression and poor interleukin (IL)-2 production. We previously showed that the expression of the transcriptional repressor cyclic AMP response element modulator α (CREMα) is increased in SLE T cells and contributes to reduced IL-2 production. Although estrogen is implicated in the onset and exacerbation of SLE, the precise nature of molecular events regulated by estrogen in immune cell function is not well understood. Here, we asked whether estrogen regulates the expression of CREMα in human T lymphocytes. We show that exposure of human T cells to 17-β-estradiol leads to a dose-dependent increase in CREMα mRNA expression, and this increase appears to be mediated through the estrogen receptors α and β. We show that the increased expression of CREMα is due to increased transcriptional activity of the CREM promoter and is mediated by increased expression and binding of the Sp1 transcriptional activator. We further show that estrogen treatment leads to a dose-dependent decrease in IL-2 mRNA and cytokine production by T cells. Finally, the effect of β-estradiol on CREMα is observed more frequently in T cells from women than from men. We conclude that estrogen can modulate the expression of CREMα and lead to IL-2 suppression in human T lymphocytes, thus revealing a molecular link between hormones and the immune system in SLE.