A 72-year-old male with delusional disorder, somatic type (DDST), was treated by modified electroconvulsive therapy (mECT). His somatic delusions were completely resolved by mECT. In parallel with the improvement of his clinical symptoms, we observed an improvement of regional cerebral blood flow (rCBF) in the left temporal and parietal lobes shown by the single photon emission computed tomograpy (SPECT). This study appears to support the utility of mECT for somatic delusions in elderly patients and suggests possible association of the dysfunction in the left temporal and parietal lobes with manifestation of the somatic delusion of the patient.