Healthy young women produce approximately 300 microg of testosterone per day, of which about half is derived from the ovaries and half from the adrenal glands. In women, as in men, testosterone is thought to influence pubertal development, sexual function, bone density, muscle mass, erythropoiesis, energy, cognitive function and mood. Testosterone deficiency in women may result from a variety of conditions, including oophorectomy, adrenalectomy, adrenal disease, pituitary disease, HIV infection, premature ovarian failure, Turner's syndrome, and the use of high-dose corticosteroids and some estrogen preparations. Simple aging and natural menopause may also contribute to testosterone deficiency in some women. A consensus view of the diagnosis of female androgen deficiency syndrome (FADS) is currently being developed, and is summarized in this article, as are current approaches for treating testosterone deficiency in women. Recent clinical trials involving an experimental testosterone transdermal patch for women are highlighted. The impact of conventional ERT/HRT on testosterone levels in naturally menopausal women is discussed, with the differences between oral and transdermal routes of estrogen delivery being emphasized.