Background: The purpose of this study was to investigate the ability of normal elderly participants and patients with Alzheimer's disease to copy the Necker cube. Method: One hundred and seventy elderly participants were randomly selected from the town of Tajiri, northern Japan, and were classified into three groups based on the Clinical Dementia Rating (CDR): CDR 0, healthy
CDR 0.5, questionable dementia
and CDR 1 and 2, mild and moderate dementia. Dementia patients (CDR 1 and 2) met the criteria of probable AD of the NINCDS-ADRDA. Using eight original criteria, we examined their ability to copy the Necker cube. Results: Most CDR 0 participants could at least succeed in copying a simple cube. About a half of the AD patients could not draw a three-dimensional figure. Among the CDR 0.5 participants, we found a 'two-peak' distribution. Conclusion: Copying the Necker cube may be one useful task for the detection of very mild Alzheimer's disease. © 2006 Japanese Psychogeriatric Society.