The aim of this study was to determine which brain structures show the greatest influence of partial volume effects (PVE) in single-photon emission tomography (SPET) studies on Alzheimer's disease (AD). Brain perfusion SPET was performed in 30 patients with probable AD and 62 age-matched healthy volunteers. SPET images were corrected for PVE using grey matter volume segmented from magnetic resonance images. The most prominent changes after PVE correction were observed in the medial temporal structures. The PVE correction revealed a selective decrease in regional cerebral blood flow (rCBF) in the parahippocampal gyrus of AD without rCBF decreases in the hippocampus, which had been observed before correction. This correction seems to be essential in order to achieve accurate measurements of rCBF in SPET, which has limited spatial resolution.