OBJECTIVE: The aim of this study was to explore the reliability and validity of the Korean version of the Cornell Scale for Depression in Dementia (CSDD-K), a scale for assessment of depression in dementia. METHODS: The original CSDD was translated into Korean and the content was verified through back-translation procedures. This study included 59 depressive patients with Alzheimer's disease (AD), 62 non-depressive patients with AD and 36 healthy elderly controls. The subjects were assessed using CSDD-K, the 17-item Hamilton Depression Rating Scale (HAM-D17), the 15-item Korean version of Geriatric Depression Scale (GDS15) and the Korean version of Mini-mental Status Examination (MMSE-K). RESULTS: In the reliability test, Cronbach's alpha coefficient and test-retest reliabilities were 0.92 and 0.91, respectively, indicating that the CSDD-K has good internal consistency. There were significant differences in CSDD-K total scores between AD patients with depression and AD patients without depression (p<0.001). In the analysis of the concurrent validity of the CSDD-K, there were significant correlations between the CSDD-K and HAM-D17 (r=0.91, p<0.001) and between the CSDD-K and GDS15 (r=0.75, p<0.001). ROC curve analysis identified a cut-off score of 7 for the CSDD-K, where the sensitivity was 87.5% and the specificity was 100%. Factor analysis resulted in a four-factor solution accounting for 63.8% of the common variance. CONCLUSION: The CSDD-K showed good reliability and validity for the assessment of depressive symptom severity in AD patients. The CSDD-K is a useful instrument for assessing AD patients with depressive symptoms in Korean ethnic population.