The sensitivity and specificity of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) single-headed single photon emission computed tomography (SPECT) in dementia were evaluated in elderly patients with a mean age of 84 years suffering from dementia (n = 59) and compared to an age- and sex-matched control group with normal cognitive function (n = 14). The demented patients were classified as suffering from primary degenerative dementia (PDD, n = 51) based on DSM-III-R criteria. Moreover, PDD patients were divided into three subgroups of severity of cognitive impairment, according to their Folstein score. Multi-infarct dementia (MID, n = 8) was diagnosed based on clinical features, computed tomographic findings and Hachinski ischaemic score. Images were assessed qualitatively by visual interpretation of shades of colour in cortical regions. A SPECT defect confined to the frontal, parietal, temporal or (parieto) occipital lobe was defined as one lesion. The mean number of SPECT lesions was 1.4 (range 0-4) in the control group, 2.4 (range 0-8) in the PDD group and 2.9 (range 2-5) in the MID group and showed a significant difference (P < 0.02) between groups. To obtain an acceptable level of specificity of 64.3%, a cut-off value of three lesions had to be chosen. In the PDD group, sensitivity was then 25% for the mildly, 43.8% for the moderately and 46.7% for the severely affected PDD subgroup. In the MID group sensitivity was then 75%. Interestingly, in this elderly patient population the location of lesions was homogenously distributed in all groups, including the control group.