Mild cognitive impairment (MCI) is a condition in which patients experience a decrease in memory and attention and often precedes Alzheimer's disease. We previously showed in a six-month long study that treatment with transdermal nicotine patches improved symptoms in MCI. In this longer, definitive two-year study, our primary hypothesis is that nicotine will enhance attention and memory in 300 patients with MCI, that this improvement will improve overall functioning, and that this difference will be sustained over two years.