This study examined the effects of unopposed estrogen replacement therapy (ERT) on the cognition and clinical course of women who have been diagnosed with probable Alzheimer’s disease. The records of 99 women diagnosed with probable Alzheimer’s disease according to NINCDS-ADRDA criteria, and in some cases autopsy confirmed as well, were analyzed. Depression, education, and age were all considered in the analysis. Results suggest that after an average of four years after symptoms appeared, women on ERT at the time of their diagnoses had similar cognitive functioning compared to those who are not on ERT. There were, however, significant differences in the clinical course of the illness between the two groups, with the non-ERT group reporting more “non-memory” problems as initial symptoms in addition to a having greater degree of overall behavioral deficit in activities of daily living.