Cognitive aging is associated with decreases in memory, attention, and visual/motor performance and skills. Dementia consists of loss of memory and other cognitive abilities, associated with social or occupational impairment. Potential neuroprotective effects of estrogen include lowering beta-amyloid, enhancing cholinergic function, promoting synaptic plasticity and nerve process growth, reducing oxidative stress, and enhancing brain glucose transport. Observational and longitudinal studies suggest that hormone therapy may attenuate age-associated cognitive impairment or decrease Alzheimer's disease but this has not been confirmed by randomized clinical trials. A critical window of time may exist around the menopause when hormone therapy may delay or decrease cognitive changes; however, hormone therapy initiated in the late postmenopause does not improve global cognition and may increase dementia risk.