Semantic dementia is a progressive neurodegenerative disorder characterized by loss of semantic memory in verbal and nonverbal domains. The most common symptom is in the verbal domain and is characterized by a progressive primary aphasia. Patients with semantic dementia sometimes exhibit surface dyslexia, a relatively selective impairment in reading low-frequency words with unusual or unusual correspondences. Semantic dementia is one of three clinical syndromes associated with anterolateral temporal lobar degeneration. Semantic dementia is a clinically specific syndrome, but it is most often associated with temporal lobe atrophy and is therefore sometimes called lobar variant anterolateral temporal lobar degeneration. The condition was first described by Arnold Pick in 1904 but in modern times its features were identified by Professor Elizabeth Warrington in 1975 but it was not given the name semantic dementia until 1989. The association with temporal lobe atrophy was noted by Professor John Hodges and colleagues in 1992 in a classic description of the clinical and neuropsychological features. Semantic dementia patients often complain of word-finding difficulties. Clinical symptoms include aphasia with fluency, anomia, poor understanding of word meanings and associative visual agnosia. As the disease progresses, behavioural and personality changes similar to those seen in frontotemporal dementia are common, although cases of 'pure' semantic dementia with few late behavioural symptoms have been described. Patients perform poorly on tests of semantic knowledge. The published tests include verbal and non-verbal tasks, for example, The Warrington Concrete and Abstract Word Synonym Test, and The Pyramids and Palm Trees task. The scans will also reveal deficits in picture naming and fluency. Structural MRI shows a distinctive pattern of atrophy in the temporal lobes with greater medial than superior and greater anterior than posterior temporal lobe atrophy. This distinguishes it from Alzheimer's disease. Analyses based on the pooling of independent MRI and FDG-PET studies have confirmed these findings by identifying alterations in the medial temporal poles and amygdala as hotspots of disease - brain regions discussed in the context of cognitive, semantic information processing and social cognition. Based on these imaging modalities, semantic dementia can be separated from other subtypes of frontotemporal lobar degeneration, frontotemporal dementia and progressive aphasia. The majority of patients with SS dementia will have ubiquitin-positive, TDP-43-positive, and tau-negative inclusions, although other pathologies have been described less frequently, notably tau-positive Pick's disease and Alzheimer's disease. Of all the frontotemporal lobar degeneration syndromes, SS dementia is the least likely to occur in families and is usually sporadic. There is currently no known cure for this condition. Supportive care is essential for a highly debilitating problem.