Subclinical thyroid disease and even variations in thyroid function within the normal range is associated with cognitive function and a risk of Alzheimer disease (AD). Several studies reported the effect of thyroid hormones on cerebral blood flow. The aim of this study was to objectively evaluate regional cerebral blood flow (rCBF) in association with thyroid hormone levels within the normal range in patients with AD. Serum thyroid-stimulating hormone (TSH), free T3, and free T4 levels were measured in 62 patients with AD (23 men and 39 women; age 56 to 91 y; mean age 77.3 y) and 27 control subjects (9 men and 18 women; age 61 to 93 y; mean age 75.8 y). The 99mTc ethylcysteinate dimer single photon emission computed tomography was performed in all subjects. The rCBF in the region of interest was measured by the noninvasive Patlak plot method and calculated using FineSRT, which is a fully automated region of interest technique. No significant correlation was found between thyroid hormone levels and Mini-Mental State Examination scores or global CBF values. Serum levels of TSH, but not free T3 or free T4, were significantly inversely correlated with rCBF in the middle and inferior temporal regions of right cerebral hemisphere in patients with AD. Control subjects showed no significant correlation between thyroid hormone levels and rCBF. Although these findings of a regional relationship must be considers preliminary, this study proposed the hypothesis that altered TSH levels within the normal range may be related to brain perfusion in right temporal region.