OBJECTIVE: The primary purpose of this study was to investigate the effects of donepezil on the behavioral and psychological symptoms of dementia (BPSD) in patients with Alzheimer's disease (AD). Additionally, its effects on cognitive function, activities of daily living (ADL) and global severity were investigated, and its safety was evaluated. METHODS: This was a 24 week prospective, open-labeled study with donepezil. The primary efficacy was measured by Behavior Pathology in Alzheimer's Disease Rating Scale (BEHAVE-AD);additional efficacies were assessed by Korean version of Mini-Mental State Examination (MMSE-K), Barthel Activities of Daily Living (BADL), Blessed Dementia Rating Scale (BDRS), and Global Deterioration Scale (GDS). Efficacy measurements were conducted at baseline and at weeks 4, 8, 12, and 24. Adverse events were rated using the UKU side effect rating scale at each time point and were monitored as well at the time of development. RESULTS: Of 40 patients recruited, 20 (50%) patients completed the study. The main reason for drop-out (N=14, 70%) was loss of follow-up. In the completers, scores on BEHAVE-AD were reduced significantly, particularly in subscales of `Activity Disturbances', `Diurnal Rhythm Disturbances', and `Affective Disturbances', while no significant changes were found in subscales of `Hallucinations' and `Anxieties &Phobias'. There were no significant changes in the scores on MMSE-K, BADL, BDRS, and GDS. Neither change was found in the scores on the UKU side effect rating scale. Although there were a few adverse events potentially associated with donepezil, they were tolerable and transient. CONCLUSIONS: Donepezil treatment was effective in some aspects of BPSD, and delayed the decline of cognitive function, ADL, and global severity in patients with AD. In addition, it was generally well tolerated in terms of adverse events.