Aims: This paper discusses the methodology and results of a three stage diagnostic procedure aimed to select demented subjects and non-demented controls for a prospective field study on the need for care and the primary care provisions for demented persons. Methods: In the first stage, simple assessment of Activities of Daily Living (ADL), Instrumental Activities of Daily Living (IADL) and behaviout were used to detect cognitive loss with great sensitivity. In the second and the third stage more specific diagnostic testing was performed among which the Mini Mental State Examination (MMSE) and finally the Cambridge Examination for Mental Disorders in the Elderly - Revised (Camdex-RN) was used to select demented subjects. At each stage a sample of test 'negative' patients were included as a control group. Results: Primary health care workers initially included 4,431 patients. In the third stage 1,036 persons were eligible for Camdex-testing of which 409 (39,5%) were diagnosed as demented, 41 (4,0%) as mild cognitive impaired (MCI) and 127 (12,3%) as depressed. Conclusions: The final study population is a well documented and relevant population to study assessment instruments for the need for care and the quality of life of demented persons and their informal care-givers.