Dementia of Alzheimer type is the most common cause of dementia in late midlife and old age. A small proportion of Alzheimer’s disease patients exibit early-onset dementia, becoming symptomatic between ages 35 and 55. It has been suggested that differences might exist between Alzheimer’s disease in early-onset and late-onset patients. The diagnosis of Dementia of Alzheimer type is made by exclusion of other causes of dementia. But the differentiation between forms of dementia on clinical grounds remains imprecise. Both X-ray CT and M RI images are as yet regarded of limited value for the clinical assessment of Dementia of Alzheimer type. Single photon emission computed tomgraphy( SPECT) studies using mTc-HMPAO have shown bilateral parietal perfusion defect and may assume importance in the clinical assessment and differential diagnosis of Alzheimer’s disease. The authors report a case of early-onset dementia of Alzheimer type which showed bilateral pariatal perfusion defect on mTc-HMPAO SPECT and suggested SPECT may be a valuable method for the clinical assessment of dementia of Alzheimer type.