Testosterone, an androgen, is viewed as a male hormone and for this reason is less studied in women than in men. In postmenopausal women, testosterone concentrations are affected by a number of factors, including age and whether a woman has undergone oophorectomy. Past hormonal exposures may also be relevant. In this chapter, Wharton, Asthana, and Gleason review research indicating that testosterone affects function of the hippocampus and other brain regions, and that testosterone has actions that might be expected to reduce Alzheimer's disease (AD) risk in women as well as men. Some studies in women suggest a relation between testosterone therapy or testosterone concentrations and performance on cognitive tasks involving visuospatial abilities. Unfortunately, few data are available on testosterone administration in women at risk for AD or with symptoms of this disorder. The authors conclude that further research is warranted on the cognitive effects of testosterone administration in older women, perhaps concurrently with estradiol and perhaps particularly in women who have experienced surgical menopause.