AIM: It was recently reported that theory of mind is disturbed in mild Alzheimer's disease dementia (ADD). Some studies have reported reduced scores of ADD patients on false belief tests, even on first-order false belief tests. However, few studies have pursued the neural substrate of false belief tests in patients with ADD in a real-world setting. METHODS: Sixty-three patients with ADD from outpatient units took the Sally-Anne test and underwent brain single-photon emission computed tomography. Of these patients, 29 answered the Sally-Anne test correctly (successful group) and 34 incorrectly (unsuccessful group). We compared the regional cerebral blood flow between the successful and unsuccessful groups. RESULTS: A comparison of the two groups showed a significantly lower uptake in the bilateral posterior cingulate gyrus in the unsuccessful group than in the successful group. CONCLUSIONS: The posterior cingulate gyrus is known to be particularly activated when individuals remember personal events and infer the mental states of others. We suppose that memory or mentalization in the posterior cingulate gyrus-or both-is essential for patients with ADD to be able to pass the Sally-Anne test.