Patterned hair loss in men and women, although medically benign, is a common, albeit unwelcome, event that may cause considerable anxiety and concern. Patterned hair loss is progressive and when untreated leads to baldness. The prevalence and severity of this physiologic process both increase with advancing age. Although androgens play a key role in the pathogenesis of male pattern hair loss (MPHL), the role of androgens in female pattern hair loss (FPHL) is less well established. Satisfactory treatment response to antiandrogen therapy supports the involvement of androgens in the pathogenesis of FPHL. Spironolactone has been used for 30 years as a potassium-sparing diuretic. Spironolactone is a synthetic steroid structurally related to aldosterone. Since the serendipitous discovery 20 years ago that spironolactone given to a woman for polycystic ovary syndrome (PCOS) and associated hypertension also improved hirsutism, it has been used as a primary medical treatment for hirsutism. Spironolactone both reduces adrenal androgen production and exerts competitive blockade on androgen receptors in target tissues. Spironolactone has been used off-label in FPHL for over 20 years. It has been shown to arrest hair loss progression with a long-term safety profile. A significant percentage of women also achieve partial hair regrowth. Spironolactone is not used in male androgenetic alopecia because of the risk of feminization.