To evaluate the possible relation between the rate of cognitive deterioration in patients with probable Alzheimer's disease (AD) and the distribution pattern of neural dysfunction. The regional cerebral blood flow (rCBF) was measured in rapidly and slowly progressing groups of AD patients using single-photon emission computed tomography and was compared between the groups. While controlling for demographic and clinical factors that could be associated with the stage and prognosis of the illness, the deterioration rate of the Mini Mental State Examination (MMSE) score was significantly greater in the rapidly progressing group than that in the slowly progressing group. The rCBF in the right posterodorsal, anterior and superior prefrontal cortices and the inferior parietal cortex was significantly lower in the rapidly progressing patients. Moreover, lower perfusion in these regions correlated significantly with rapid deterioration in the MMSE. These findings suggest that the rCBF values in these cortical regions could be useful in predicting which AD patients will show a relatively rapid cognitive decline.