We report an autopsy case of MM1-type sporadic Creutzfeldt-Jakob disease (sCJD) with an unusually prolonged disease duration of 58 months. The initial symptom was progressive mental disorder followed by advanced cognitive impairment. Clinical progression was generally slow; myoclonus appeared at 17 months and periodic sharp-wave complexes on electroencephalogram at 21 months. A state of akinetic mutism occurred 29 months after the onset of symptoms. MRI showed gradually progressive cerebral atrophy. Neuropathologic examination showed widespread severe brain involvement. In the cerebral neocortex, widespread severe tissue rarefaction, hypertrophic astrocytosis and neuron loss (so-called status spongiosus) were observed. The cerebral white matter showed diffuse myelin pallor with intense hypertrophic astrocytosis, numerous foamy macrophages and emperipolesis, indicating panencephalopathic-type sCJD pathology. The brainstem was relatively preserved from sCJD pathology, with the exception of the pontine nucleus and pyramidal tract. This may explain the prolonged disease duration without respiratory insufficiency until the terminal stage. Immunohistochemistry for prion protein (PrP) showed widespread synaptic-type PrP deposits in the cerebral neocortex, hippocampus and thalamus. The striatum and cerebellar cortex showed faint synaptic-type PrP deposition with some areas of small plaque-like PrP deposition. Sparse PrP deposition was also observed in the brainstem. Analysis of the PrP gene showed no mutation but methionine homozygosity at polymorphic codon 129. Western blot analysis of protease-resistant PrP indicated type 1 PrP. To our knowledge, this is the longest reported disease duration of MM1-type sCJD.