Dementia syndromes constitute problem not only for the elderly. Early-onset dementia (EOD) starts below the age of 65 years. It accounts for 4–10% of all cases of dementia. EOD has significant psychosocial consequences because it affects people in their most productive years of life, with numerous family, professional and social responsibilities. There are many diseases that have been identified as the cause of the EOD. Among them, the most common are Alzheimer’s disease, vascular dementia, fronto-temporal dementia, Lewy body dementia, traumatic brain injury, alcohol related dementia, Huntington’s disease, Parkinson’s disease, mixed dementia, Creutzfeldt-Jakob disease and Down’s syndrome. Most studies have demonstrated Alzheimer’s disease as the most common etiology of EOD. The article presents the case of a 33-year-old patient hospitalized in the Department of Neurology in Zabrze, with cognitive dysfunction, speech disordersand featuresof Parkinson’s extrapyramidal syndrome that have been progressing for about 15 months. The MR of the head revealed cortical and subcortical atrophy, especially in parietal and temporal lobes. The cerebrospinal fluid examination showed decreased level of β-amyloid and significantly elevated level of H-tau. The patient was diagnosed with early-onset Alzheimer’s disease, which was confirmed by genetic testing – the sequence change was identified in the gene for presenilin 1 in a heterozygous system.