Normative data were collected in a study population of 150 randomly selected elderly subjects. Using the SIDAM (Structured Interview for the Diagnosis of Dementia of the Alzheimer Type, multi-infarct dementia, and dementias of other etiology according to DSM-III-R and ICD-10), both the dimensional and the categorical aspects of dementia and “mild cognitive impairment” are considered. With the SIDAM score (SISCO) [range 0 (minimum)-55 (maximum, no cognitive impairment)] and the SIDAM Mini-Mental State Examination (MMSE) (range 0–30), appropriate cutoffs for the category of DSM-III-R and ICD-10 dementia and “mild cognitive impairment” were defined. MMSE scores of 0–22 were found to be indicative of DSM-III-R and ICD-10 dementia. For “mild cognitive impairment,” MMSE scores ranged from 23–27 according to a DSM-III-R definition (ICD-10: 23–28). An MMSE score of 22 or less was found to differentiate between DSM-III-R/ICD-10 dementia and “mild cognitive impairment,” with a specificity of 92% (ICD-10: 95.6) and a sensitivity of 96% (ICD-10: 96%). With the SIDAM-based DSM-III-R/ICD-10 diagnoses of dementia as the criterion, the SISCO was 97.3% specific (ICD-10: 99%) and 94% sensitive (ICD-10: 94%) in detecting dementia. A SISCO of 0–33 was highly indicative of DSM-III-R and ICD-10 dementia. For “mild cognitive impairment,” a SISCO between 34–47 (ICD-10: 34–51) was found. The SISCO covers a broader range of cognitive functions that the MMSE and is more useful in detecting even very mild cognitive decline. Furthermore, the newly defined category of “mild cognitive impairment” could be validated successfully by means of GDS Stages 2–3 and CDR Stage 0.5. These findings confirm the value of the SIDAM as a short diagnostic instrument for measurement and diagnosis of dementia and “mild cognitive impairment.”