This study is an observational study conducted prospectively under routine clinical setting for 1 year with about 700 patients diagnosed as Alzheimer's disease who will be treated by donepezil (Aricept) as monotherapy. The subjects will be recruited in the selected institutions of about 8 countries in Asia.

Participation in this study places no additional visit schedule, which will be determined by the investigator's judgment based on the disease progression of each subject. Investigators educate subjects to keep decided visit schedule, and collect the required information for case record from (CRF) on the visit.

Inclusion Criteria:

1. Greater than or equal to 50 years old and less than 90 years old
2. Diagnosed as probable AD based on NINCDS-ADRDA
3. Patients who have been recently prescribed with donepezil (Aricept) as monotherapy
4. Patients and caregivers who signed the written informed consent from for use of personal and medical information
5. Patients with caregivers who can visit the institution together

Exclusion Criteria:

1) Patients who have taken Memantine or Acetylcholinesterase (AChE) inhibitor prior to participating in the study

Alzheimer's disease patients who have been recently prescribed with donepezil (Aricept) as monotherapy for the first time