Electroencephalographical studies have disclosed correlations between topographical features of Fast Fourier Transformation maps and the severity of Alzheimer's disease (DAT). The object of the present study was to explore the relations of HMPAO-SPECT and quantitative EEG (qEEG) with the severity of dementia. Twenty-three patients were included in the study. Spectral and topographical EEG parameters were compared with global and regional cerebral blood flow, and with psychometric measures of clinical severity. None of the regions of interest of the SPECT scans were significantly correlated with clinical severity. Low values in delta- and theta bands, however, were related to high scores on the Mini-Mental-State examination (P < 0.01), whereas the Syndrome-Kurz test correlated inversely with the power values in the alpha and beta band. The global decrease in cerebral blood flow (CBF) was associated with a shift on the topographical alpha-centroids in the posterior direction (P < 0.01). In previous studies correlations between CBF and clinical severity were weak, indicating a high interindividual variance, or interactions with concomitant vascular lesions. Whereas SPECT is a well-established tool for the diagnosis of dementia, the present study indicates qEEG as a potential marker for the staging of the cognitive decline in DAT.