The aim of this study was to evaluate the ability of a trained primary health care (PHC) nurse to discriminate dementia, by systematic assessments, from other psychogeriatric diseases. The reported study emanates from a dementia prevalence survey in an elderly (65+) population (n = 851). Forty-two frail elderly people (mean age 77.8 years) referred to a psychogeriatric hospital for further clinical investigation were tested. Dementia rating scales were used by the trained nurse, who noted her clinical observations systematically as well. The instrument results of the testing procedures, evaluated in combination with the clinical picture of the patients, were correlated to the DSM-III-R criteria of dementia. Thereafter, the nurse's judgments were compared with the clinical diagnoses based on thorough geropsychiatric investigations. The nurse's diagnoses of moderate and severe dementia had a sensitivity of 80% and a specificity of 82%. The predictive value of a positive test for moderate and severe dementia was 87%. When the mildly demented patients were included, sensitivity was 93%, specificity was 75%, positive predictive value was 90%, and kappa value was. 70.