Recent data report an important role of testosterone (T) in modulating female sexual responses, but little is known about the expression and distribution of androgen receptor (AR) in the human vagina. Therefore, the aims of our study were to evaluate the expression of AR in the human vagina in premenopausal (PrM) and menopausal (M) women and in T-treated women. Vaginal biopsies were obtained from PrM and postmenopausal women and from women with gender identity disorder (female to male (FtM)) receiving exogenous T. AR gene and protein expression levels in vaginal tissues were determined by real-time PCR and western blot analysis, respectively, whereas the localization of AR in vaginal mucosa and stroma was performed by immunohistochemistry. ARs were detected by immunostaining both in the mucosa and stroma. In vaginal mucosa, AR density score decreases with age but does not change with T administration. In stromal tissue, AR density score does not change with age but significantly increases with T administration (P<0.01). AR protein expression was significantly increased in FtM subjects (P<0.001). The expression of AR messenger RNA (mRNA) evaluated by Real-time PCR showed a significantly higher mRNA expression in FtM versus M patients (P<0.01) and in PrM versus M subjects (P<0.05). In conclusion, we found AR protein and mRNA expression both in the epithelium and stroma of the human vagina in all groups of women. A negative correlation exists between age and AR expression in the vaginal mucosa. T administration increases AR expression in both the mucosa and stroma.