The study is a validation study of two psychogeriatric depression rating scales, The Geriatric Depression Scale (GDS) and the Cornell Scale for Depression in Dementia (CSDD). The sensitivity and specificity, and the convergent and criterion validity of the two scales as well as the inter-rater reliability of the CSDD are reported. Two independent clinicians using the ICD-10 for depression and dementia, the Clinical Global Impression (CGI), the Hamilton Depression rating scale 17-items and the Mini-Mental-State Examination (MMSE), interviewed each patient or control subject. One hundred forty-five persons of 65 years or more of age were included, 73 were depressed only, 36 depressed and demented; 36 persons were control subjects, 11 of these were demented. The inter-rater reliabilities were high or very high equalling perfect correlation. There was very high convergent validity between the screening tools and the severity scales; the shorter versions of the GDS (15-, 10- or four-item version) had lower though still almost perfect correlations. The criterion validity in the total population showed the CSDD as the better scale with sensitivity and specificity of 93% and 97% with a cut-off value of > or =6. The GDS versions had sensitivities and specificities ranging from 82% to 90% and 75% to 94% respectively with cut-off values > or =9, 4, 3 and 1. The CSDD retained its validity and specificity as a screening tool for depression in a population of demented, while the GDS versions all diminished in validity. The GDS and the CSDD are both valid screening tools for depression in the elderly; however, the CSDD alone seems to be equally valid in populations of demented and non-demented.