Androgens play an essential role in the corporo-venous occlusive mechanism that provokes erection. Accordingly to various studies based on animal models,testosterone deficit syndrome causes an endothelial disorder in the corpora cavernosa with diminished secretion of NO, alteration of penile smooth muscle and tunica albuginea structure, and increase of the number of adipocytes within the erectile tissue, which favors fibrosis and impairs erection. All these alterations are reversible with the exogenous administration of androgens. There are not enough studies to get definitive conclusions about androgen supply improving erectile dysfunction in patients with hypogonadism. Studies have been published in which seems that exogenous testosterone could be useful in the treatment of this type of patients. Nevertheless,in most published randomized double blind studies comparing with placebo, testosterone supply does not provide greater benefit on erectile dysfunction than PDE-5 Inhibitors exclusively. All studies coincide in the need to optimize the treatment with PDE-5 Inhibitors since they do have proven to be effective for the treatment of erectile dysfunction in patients with testosterone deficit syndrome.