BACKGROUND: Apathy is one of the most frequent behavioral symptoms in Alzheimer's disease (AD) and interferes with activities of daily living. The purpose of this study was to evaluate the differences of cerebral blood flow between AD without apathy and with apathy. METHODS: Nineteen AD patients without apathy (AD-NA group) and 15 AD patients with apathy (AD-A group) were evaluated. Cerebral perfusion was measured by (99m)Tc-ECD single photon emission computed tomography (SPECT). The images of the AD-A and AD-NA groups were statistically analysed by means of statistical parametric mapping (SPM) 99. RESULTS: Compared with AD-NA group, the AD-A group had significantly lower perfusion in the left inferior frontal regions (left orbital gyrus, Broadmann area 47 and left median frontal gyrus, Broadmann area 11) (uncorrected p<0.01). CONCLUSIONS: These results suggest apathy may be related with disturbances in projections of frontal subcortical circuits, even though apathy is primarily related with dysfunction of the cingulate gyrus.