OBJECTIVES: The purpose of this study was to compare the efficacy between switching patients with Alzheimer's disease (AD) from galantamine or rivastigmine to donepezil because they were not responding adequately, and naive patients with AD who initiated therapy with donepezil. METHODS: A total of 108 patients were recruited for this 52-week study. The effect of donepezil on cognitive function was measured using Alzheimer's Disease Assessment Scale-cognitive subscale-preliminary Korean version (ADAS-cog-K). Patients' activities of daily living using Seoul-Activities of Daily Living (S-ADL) and the Seoul-Instrumental Activities of Daily Living (S-IADL);behavioral symptoms using the Korean version Neuropsychiatric Inventory (K-NPI) were measured at baseline, 13-weeks, 26-weeks, 39-weeks and 52-weeks. We defined the responsive patients to donepezil at those who showed a cognitive improvement or no change during the first six-month clinical trial. RESULTS: 86 naive patients and 22 switching patients were enrolled in the study. 74 patients completed the study and 34 discontinued their treatment before week 52. There was no significant difference between two patient groups in demographic data, baseline characteristics and dementia severity except duration of illness. The total ADAS-cog-K scores were not significantly different from baseline after 52 weeks of treatment in both groups. Both groups demonstrated deterioration of S-ADL and S-IADL at 52 weeks. The NPI scores did not significantly change in both groups. Based on the operational criteria, 61.6% of the naive group and 54.5% of the switching group were responders to donepezil. CONCLUSION: The switching group had similar levels of efficacy with the naive group who initiated therapy with donepezil. These results suggest that patients not responding adequately to rivastigmine or galantamine may improve or stabilize after switching to donepezil and prior medication does not effect donepezil's efficacy.