Transforming growth factor beta 1 (TGF-β1) is a key regulator that modulates male reproductive function. Testicular TGF-β1 modulates the steroidogenesis of Leydig cells, the organization of peritubular myoid cells, testis development and spermatogenesis. Several studies have indicated that TGF-β1 is involved in the tight balance between proliferative and apoptotic responses in the Leydig cells. In the present review, we summarize the direct effects of this cytokine in Leydig cells under normal and pathological conditions. We analyze the effect of TGF-β1 inLeydig cells depending on the type of receptors involved in the signaling pathway of TGF-β1. Our group has been analyzing the canonical and non canonical intracellular signaling pathways of TGF-β1 that are involved in the expression of proliferative and apoptotic markers in Leydig cells. On the basis of our studies and from those of other authors we conclude that the balance between the expression of TGF-β1 receptors and co receptors is of relevance in Leydig cell physiology and pathophisiology.