BACKGROUND: Addenbrooke's Cognitive Examination (ACE) is a cognitive screening test developed to detect dementia. It has been validated in several countries. Validation studies have predominantly included patients with various degrees of dementia and healthy controls. OBJECTIVE: The aim of this study was to evaluate the Danish version of ACE as a screening test for early dementia in an outpatient memory clinic. Further, we wanted to investigate the ability of the ACE to discriminate patients with early Alzheimer's disease (AD) from patients with depression. METHOD: 78 patients with mild AD (MMSE >or=20), 30 non-demented patients diagnosed with depression (originally referred for evaluation of cognitive symptoms), and 63 healthy volunteers, all between 60 and 85 years of age, were included. All patients were given the ACE as a supplement to the standard diagnostic work-up. RESULTS: The cut-off points for optimal trade-off between sensitivity and specificity for ACE were 85/86 (sensitivity 0.99, specificity 0.94). When these cut-off points were applied to the group of depressive patients, the specificity dropped to 0.64, indicating a great overlap in individual test scores for demented and depressed patients. CONCLUSION: The optimal cut-off points for ACE found in this Danish study were close to what is reported in most other European studies. The great overlap in ACE scores for demented and depressed patients emphasize that test scores must be interpreted with great caution when used in diagnostic work-up.