Semantic dementia (SD) is characterized by an assymetric atrophy of the temporal lobes and, clinically, by an impairment of the semantic memory associated to psychobehavioral symptoms. The concept of SD was defined in 1989 and still remains controversial. Some authors consider DS as a specific entity, others as part of the frontotemporal dementia (FTD) or a variant of the progressive aphasia syndrome. Many arguments tend to include SD in the FTD. However, SD presents a high interest for the comprehension of the organization of semantic memory in man, and is often associated with specific histopathologic lesions (ubiquitine positive and tau negative). Therefore SD should be considered as a clinical specific entity.