Several studies have shown that the symptomatology and the neuropathological and neurochemical changes of early-onset Alzheimer's disease (EAD) differ from those of late-onset Alzheimer's disease (LAD). The aim of the present study is to examine differences in SPECT and MRI findings between EAD and LAD. Cerebral blood flow and patterns on SPECT, and deep white matter lesions and cerebral atrophy on MRI in 17 patients with EAD were compared with 30 patients with LAD without cerebrovascular risk factors. Temporoparietal activity ratio, divided by cerebellum, on SPECT imaging in patients with EAD was significantly lower than in patients with LAD. In a qualitative assessment of perfusion patterns, bilateral temporoparietal hypoperfusion, which is typical in AD, was seen more frequently in patients with EAD than in those with LAD. Among white matter changes in MRI, the score of white matter hyperintensity was significantly higher in LAD than in EAD patients. However, there was no significant difference between periventricular hyperintensity scores. Though ventricular enlargement did not differ significantly in EAD and LAD, cortical atrophy scores in LAD were significantly higher than in EAD. Cortical atrophy scores were significantly higher in patients with atypical perfusion patterns on SPECT, (e.g. global hypoperfusion in addition to temporoparietal change), than in patients with typical perfusion pattern. These results indicate that functional and morphological imagings in LAD differ with those in EAD, probably due to less-prominent neuropathological degeneration combined with age-related alterations.