Transcranial sonography (TCS) of the brain parenchyma detects alterations in the substantia nigra (SN), raphe nuclei and basal ganglia; this technique has been established as a tool for the early diagnosis of Parkinson's disease and differential diagnosis from atypical parkinsonian syndromes. Here, we aimed to review the main applications of TCS in neurodegenerative diseases presenting with dementia syndrome, focusing on Alzheimer's disease (AD), dementia with Lewy bodies (DLB), frontotemporal lobar degeneration, idiopathic normal pressure hydrocephalus, and atypical and secondary parkinsonisms. The finding of bilaterally marked hyperechogenicity of the SN appears as a characteristic feature of DLB, while it is found only in a minority of AD patients. SN hyperechogenicity is also detected in most patients with corticobasal degeneration and in about one third of patients with progressive supranuclear palsy, in which is constantly associated with hyperechogenic alterations of the basal ganglia. In conclusion, TCS is a valid supportive tool in the diagnostic workup of patients with dementia due to different neurodegenerative conditions. A promising new application is the differentiation of DLB from AD even at the early stages of these diseases.