Introduction: Brain imaging with F-18 fluorodeoxyglucose (F-18-FDG) positron emission tomography or Tc-99m hexamethylpropyleneamine oxime (Tc-99m-HMPAO) SPECT is widely used for the evaluation of Alzheimer's dementia (AD); we aim to assess superiority of one method over the other. Methods: Twenty four patients with clinical diagnosis of Alzheimer disease underwent F-18-FDG PET and Tc-99m-HMPAO SPECT in order to assess the zones of hypo metabolism & hypoperfusion specific for Alzheimer's disease. Results: F-18-FDG PET showed specific zones of hypometabolism in 19 patients (79.1%) while SPECT was positive in 15 cases (62.5%) with statistically significant difference (P=0.027). Conclusion: F-18-FDG PET was significantly superior to HMPAO SPECT and F-18-FDG PET could replace the classic role of perfusion SPECT in diagnosis of Alzheimer's disease.