Visuoperceptual processing is impaired early in the clinical course of Alzheimer's disease (AD). The 15-Objects test (15-OT), a visual discrimination task based on the Poppelreuter test consisting on 15 overlapping objects, detects such subtle performance deficits in Mild Cognitive Impairment (MCI) and mild AD. Single Photon Emission Tomography (SPECT) studies have reported reduced brain perfusion in temporal, parietal and prefrontal regions in early AD and MCI. The aim of the present study was to confirm the role of the 15-OT in the diagnosis of MCI and AD, and to investigate the brain perfusion correlates of visuoperceptual dysfunction in subjects with MCI, AD and normal aging. For this purpose, 42 AD, 42 MCI and 42 control subjects underwent a brain SPECT and separately completed the 15-OT. Results showed that the 15-OT performace was impaired in MCI and AD patients. In terms of SPECT scans, AD patients showed reduced perfusion in temporal-parietal regions, while MCI subjects had decreased perfusion in the middle and posterior cingulate. When MCI and AD groups were compared, a greater brain perfusion reduction was found in temporo-parietal regions in AD than MCI. In the whole sample, 15-OT performance was significantly correlated with clinical dementia rating scores, and with perfusion in the bilateral posterior cingulate and the right temporal pole, with no significant correlation in each separate group. Our findings suggest that the 15-OT performance provides a useful gradation of impairment from normal aging to AD, and it seems to be related to perfusion in the bilateral posterior cingulate and the right temporal pole.