It is sometimes difficult to distinguish between dementia with depressive mood and depressive pseudodementia (DPD). However, it is important that a differential diagnosis between them is made because cognition and memory disorder in DPD patients are treatable. Herein, we describe a case of senile depression in a woman with memory and cognition problems. Her diagnosis was based on low blood flow and low metabolism in her frontal lobe, detected by N-isopropyl-P-[123I]-iodoamphetamine single photon emission computed tomography (SPECT) and 18F-fluorodeoxyglucose positron emission tomography (PET). After antidepressant therapy, the patient's depressive mood diminished and blood flow and metabolism in the frontal lobe recovered. These findings suggest that SPECT and PET can be used to make a differential diagnosis between senile depression and dementia, as well as for following recovery from a depressive mood.