Each subject with MCI will be randomly assigned to treatment with either Exelon or placebo. Subjects assigned to Exelon will receive 1.5 to 6.0 mg bid (twice daily) (3.0 to 12 mg/day) for the majority of the study. At every regular visit scheduled every three months, patients will be given basic efficacy and safety assessments. These assessments will include evaluation of adverse events, vital signs, activities of daily living, and clinical staging scales to determine if the subject may have converted to dementia.