A 28-Week Open Label Extension Study Evaluating Safety and Tolerability of Donepezil Hydrochloride in Subjects With Mild Cognitive Impairment

Inclusion Criteria: 1. Age Range: Adult subjects (45 to 90 years of age inclusive) 2. Sex distribution: Men and women. Women of child-bearing potential (\<1 year post menopausal) must be practicing effective contraception and have negative serum B-HCG at Screening. \[Women who are breast-feeding are excluded.\] 3. Subjects must have completed the one year, double-blind core trial (E2020-A001-412). 4. A completed Diagnostic Worksheet at the end of the double-blind core trial (E2020-A001-412) indicating no conversion to Alzheimer's Disease or dementia. 5. Health: Generally healthy and ambulatory or ambulatory-aided (i.e., walker or cane). 6. The subject must be expected to complete the entire study. 7. Subjects must be sufficiently fluent in English. 8. Subjects must have an informant who has daily contact with the subject (e.g., an average of 10 or more hours per week), can observe for possible adverse events and will accompany the subject to all visits. 9. Clinical laboratory values must be within normal limits, or if abnormal, judged clinically insignificant by the investigator (not likely to cause cognitive impairment or medical instability). Exclusion Criteria: 1. Subjects who have not completed or have terminated early from the one year, double-blind core trial (E2020-A001-412). 2. Any subject without a completed diagnostic worksheet from Week 51 of the core double-blind trial (E2020-A001-412). 3. Any subject with a completed diagnostic worksheet from Week 51 of the core double-blind trial (E2020-A001-412) indicating conversion to Alzheimer's or other dementia. 4. Subjects with uncontrolled hypertension (sitting systolic \>= 160mmHg and/or diastolic \>=95mmHg) as assessed by the investigator, regardless of whether or not the subject is taking anti-hypertensive medications. 5. Subjects with a history of malignant neoplasms treated within five years prior to study entry (other than basal or squamous cell carcinoma of the skin); current evidence of malignant neoplasm; or recurrent or matastatic disease. 6. Subjects who have suffered a severe infection or a major surgical procedure within three months prior to baseline. 7. Subjects who may not be able to comply with the protocol. 8. Subjects with known hypersensitivity to piperidine derivatives or acetylcholinesterase(AChE)inhibitors. 9. Subjects with diabetes mellitis not controlled by diet and/or medication with a random serum glucose value of \>170mg/dl. 10. Any condition which would make the subject, in the opinion of the investigator, unsuitable for the study. 11. Subjects who do not have a reliable informant (e.g., the informant has contact with the subject less than 10 hours per week).