The authors describe the clinical characteristics, MRI abnormalities, and molecular findings in a patient with a novel variant of a two-octarepeat insertion mutation in the prion protein gene. This patient presented with moderately progressive dementia of presenile onset and gait ataxia. MRI showed extensive cortical atrophy and white matter abnormalities. The mutation consists of a two-octarepeat insertion mutation and irregularities in the nucleotide sequence of the octarepeat region.