Résumé : Partial or complete unawareness of deficits in Alzheimer‘s disease (AD) may result in delaying diagnosis and difficulties for caring. Many theories have been proposed to explain unawareness of neurological or cognitive deficits. Neurological theories use the term of anosognosia to describe unawareness as a consequence of the severity and location of brain lesions. They predict an association between the unawareness of deficits in AD and the severity of dementia or location of the lesions in the right cerebral hemisphere or in the frontal regions. More recent theories have been based on models derived from cognitive neuropsychology. Some models have been designed to explain unawareness of specific deficits such as the memory disorders, others are more extensive based on models of consciousness of the Self. Psychopathological theories postulate that unawareness of deficits is the consequence of a psychological defense mechanism, termed denial. Therefore, unawareness of deficits in AD should be linked to the premorbid personality, abilities to cope with the disease and its consequences more than to the severity and location of brain lesions. The validity of each theory is discussed according to the data from the literature. However, the analysis of the literature is clouded by many methodological difficulties due to the variability of terminology and tools used to assess the unawareness. Moreover, most studies were too narrowly focused on specific points, not taking into account a global model of insight. Nevertheless, some conclusions can be drawn from the available data: 1) the nature of the unawareness of deficits in AD is multidimensional. Terms such anosognosia or denial do not describe single phenomena but correspond to disturbances of various neurological, neuropsychological and psychopathological mechanisms, which can not be explained by a single theory; 2) unawareness should no more be considered as a category but according to a dimensional approach. There is a wide range of levels of unawareness, which can vary from one moment to an other and during the progression of the disease; 3) neurological, neuropsychological and psychopathological mechanisms implicated in unawareness probably coexist in various degrees depending, on one hand, on the disease severity and type of deficits and, on the other hand, on the history and personality of the patient, his(her) familial support, but also on the social perception of the disease. To improve our understanding of the unawareness of deficits in AD, we propose to come back to a detailed clinical description investigating extensively the various aspects of insight.