The SIDAM--a new instrument for the symptomatic diagnosis and measurement of dementia according to DSM-III-R and ICD-10--is described. It comprises a brief structured clinical interview, a range of cognitive tests (e.g. including the Mini-Mental State (Folstein et al. 1975)) which constitute a short neuropsychological battery and a section for clinical judgement and third party information. All items rely on DSM-III-R and ICD-10 algorithms. The SIDAM has a high overall test-retest reliability which equally holds true on the diagnostic, criterion and item level. It is a brief (average of 28 min), practical and easily scored diagnostic instrument, which reliably separates subjects with DSM-III-R and ICD-10 dementia from those without such a disorder. Good congruence was found between SIDAM diagnoses and corresponding ICD-9 expert diagnoses. Furthermore, the SIDAM-Score (SISCO) allows a detailed measurement of even low levels of cognitive impairment and provides quantification of severity grading of cognitive dysfunction.