The familial form of the Creutzfeldt—Jakob disease (ffCJD) refers to a group of rare and severe neurodegenerative diseases associated with pathologic prion protein accumulation. The cause of disease is genetically determined. The disease has a continuously progressive course leading to death in 100% of cases. The symptoms of dementia dominate in the clinical picture. The authors describe a clinical case of subacute dementia in a 32-year-old patient. The disease had a progressive course. A preliminary diagnosis of ffCJD was established after neurological, psychiatric, genetic examinations and dynamic observation. The diagnosis met the following criteria of the Center for Disease Control and Prevention, CDC: progressive dementia, extrapyramidal disorders, absence of special EEG complexes, disease duration less than 2—3 years, confirmed genetic mutation in the prion protein gene, bilateral hyper intensive signals in the caudate nuclei region, the thalami on T2-weighted images (a «honeycomb» symptom), atrophy of the cerebral cortex and cortex cerebelli on diffusion-weighted brain MRI (DWI). The patients died 3 years after the onset of the disease. The pathological signs of neuron spongiform degeneration as important characteristics of the disease were found at autopsy.