A 64-year-old Japanese woman with Gerstmann-Sträussler-Scheinker syndrome (GSS) is reported. She was admitted to our hospital for progressive amnesia, twitching of the right upper limb, and difficulty in speaking and walking for 5 months. Physical examination revealed a fever, tachycardia, and hyperhidrosis without any evidence of inflammation or infection. Neurological examinations demonstrated dementia, frontal lobe signs, and spontaneous myoclonus. She developed akinetic mutism 4 months later. The levels of neuron-specific enolase and 14-3-3 protein were elevated in the cerebrospinal fluid, and serial EEG showed periodic synchronous discharges. DNA analysis of the prion protein gene revealed a Pro102Leu mutation and therefore she was diagnosed as GSS102. Head MRI showed abnormal high signal intensity by T2 weighted image in bilateral caudate nuclei, putamen, frontal lobes, and white matter around the posterior horn of lateral ventricles at admission, and extension to global cerebral cortex and diffuse deep white matter with marked atrophy of bilateral frontal and cerebellar cortices 4 months later. In 123I-IMP SPECT study, uptake of RI decreased slightly only in left frontal region at admission, but decreased markedly in bilateral frontal region 4 months later. Analysis of autonomic function (analysis of noradrenarine in plasma and urine, coefficient of variation of R-R intervals before and after giving atenolol, Aschner's eyeball pressure test, intracutaneous atropine and adrenaline injection test) revealed sympathetic hyperactivity but normal parasympathetic activity. This is a very rare case of GSS102 with atypical MRI findings and clinical features like Creutzfeldt-Jakob disease rather than GSS102, presenting hyperthermia, tachycardia, and hyperhidrosis caused presumably by sympathetic hyperactivity as well as fatal familial insomnia. Therefore it is suggested that some factors besides the codon mutation in the prion protein gene may influence clinical symptoms in prion disease.