Dementia is a very serious personal, medical and social problem. Early and accurate diagnoses seem to be the key to effectively cope with it. This paper presents a diagnostic tool that couples the most widely used computerized system of cognitive tests in dementia research, the Cognitive Drug Research system, with the naive credal classifier. Although the classifier is trained on an incomplete database, it provides unmatched predictive performance and reliability. The tool also proves to be very effective in discriminating between Alzheimer’s disease and dementia with Lewy bodies, which is a problem on the frontier of research on dementia.