Alzheimer's disease (AD) is the most common cause of dementia. Frontotemporal lobar degeneration (FTLD), although less prevalent overall, is almost as common as AD in patients under the age of 65. AD and FTLD are histopathologically distinct, with AD being characterised by extracellular amyloid plaques and intraneuronal neurofibrillary tangles, and FTLD by the presence of non-AD histological pathology, most commonly either tau-positive inclusions or ubiquitin-positive or TDP 43 positive inclusions. Clinically, AD and FTLD may occur with overlapping symptoms, especially in the early stages of the disease. In the case of Alzheimer's disease, it is represented by isolated decline of recent episodic memory; later on, by the impairment of time and space orientation, whereby the alteration of social behaviour and amnesic aphasia occur predominantly in the advanced phases of the disease. Frontotemporal lobar degeneration is demonstrated in three clinical subunits: 1) The behavioural-dysexecutive variant of FTLD (frontotemporal dementia, the frontal variant of FTLD, {fvFTLD}), 2) Progressive non-fluent aphasia, 3) Semantic dementia (SD) with the profound impairment of social conduct (fvFTLD) or with severe speech impairment (PNFA, SD). Considering the different clinical symptomatology with FTLD diagnostics, it is necessary to use different psychometric tests than in the case of Alzheimer's disease. Therapy and the degree of dependence of the affected person are also different. All three diseases within the FTLD category, mainly the behavioural-dysexecutive variant, require a higher level of nursing care on the part of other persons or institutions in comparison with Alzheimer's disease. The goal of our publication is to point to the differences in clinical manifestation and the findings of auxiliary examinations that are helpful in the clinical accuracy of the distinction between these two types of dementia (Tab. 1, Fig. 3, Ref. 18).