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Semantic dementia (SD) is a syndrome of progressive loss of semantic knowledge for objects and people. International criteria propose that SD be included in the frontotemporal lobar degeneration syndromes, with progressive non-fluent aphasia and frontotemporal dementia (FTD). However, several related syndromes have been defined that clinically and conceptually share both similarities and differences with SD: fluent progressive aphasia, progressive prosopagnosia, temporal variant of FTD. In order to establish a French consensus for the diagnosis and modalities of evaluation and follow-up of SD, a working group, composed of neurologists, neuropsychologists and speech-therapists, was established by the Groupe de reflexion sur les evaluations cognitives (GRECO). New criteria were elaborated, based on clinical, neuropsychological, and imaging data. They define typical and atypical forms of SD. A diagnosis of typical SD relies on an isolated and progressive loss of semantic knowledge, attested by a deficit of word comprehension and a deficit of objects and/or people identification, with imaging showing temporal atrophy and/or hypometabolism. SD is atypical if the deficit of semantic knowledge is present only within a single modality (verbal versus visual), or if non-semantic deficits (mild and not present at onset) and/or neurological signs, are associated with the semantic loss.