It is generally accepted that presenile Alzheimer's disease (AD) has faster progression and severer clinical manifestation than senile onset AD. Recently a relative left frontal hypoperfusion was only found in patients with presenile AD by using SPECT imaging. The aim of the present report was to ascertain whether the same conclusion could be drawn matching the population with respect to the severity of the cognitive profile and disease duration. Twenty subjects for each group were studied with SPECT and no differences emerged between groups. It is postulated that presenile and senile onset AD represent aspects of the same biological process.