This Article deals with the question of ignorance after a serious brain injury. The main purpose of this research is to present some factors that are critical for the differential diagnosis of anosognosia (organic etiology) and denial (psychological etiology) in order to improve the rehabilitation strategies of brain injuried population. In the present work we report the case study of MG (Havet-Thomassin, 2000). MG is a 32 Year old right handed man who has undergone a severe brain injury after a car accident. Neuropsychological approach of ignorance is mainly landed from questionnaire assessment of deficit. The QAM (Questionnaire of self assessment of memory performance, Van der Linden et al., 1988) and the PCRS (Patient Competency Rating Scale, Roueche et Fordyce, 1982) where used for the neuropsychological assessment of anosognosia. The neuropsychological baseline was obtained from classical executive tasks (TMT, Stroop, TOL, WCST) in order to show a possible link between executive dysfunction and anosognosia. The results point several cognitive impairments (attention, memory, executive functions) and an inadaptated behavior associated to an important anosognosia particularly at the beginning of the hospitalization (absence of self-criticism and bad compliance to rehabilitation). Furthermore, the patient was interviewed regularly in order to better dissociate denial from anosognosia. This clinical approach facilitated the understanding of the inherent psychological dynamic of MG which was particularly exacerbated by the frontal desinhibition. Characterization of identity profile and homosexuality are of great interest in this case as they were strongly reactivated by the traumatism. The brain injury leads to the reorganization of the whole identity of MG which seems no more unified but divided. Reality principle was responsible for too much anxiety which became probably acute by a narcissistic flaw. Therefore it encourages the subject to deny in order to guarantee to himself a psychic balance. Thus, at the beginning, MG denies totally his homosexuality and then, he admits it progressively declaring that it has disappeared since the accident. He progressively developed an excessive aggressiveness in regard of the homosexual community insinuated unconsciously from his discourse his feminine and passive position (slips, denegations). This denial is critical for MG's psychic integrity and that is why the priority should not be its suppression. From this work, we consider that anosognosia remains independent of the patient's will, but still linked to the dysexecutive syndrom. In opposite, the denial corresponds to defensive and strategic processes devoted to the subject adaptation to an agonizing situation. Even if those two clinical facts appear similar, it is possible to propose several factors in order to distinguish anosognosia from denial: 1) anosognosia and denial don't seem to turn on the same elements; 2) anosognosia seems to be more transitional on the contrary of the denial which appears to be more chronic; 3) behavior reaction in the case of anosognosia seems to be partially different from the denial; 4) as compared to anosognosia, denial appears less stable and more uncertain depending on the psychic cost. In conclusion, distinction between anosognosia and denial would allow the clinical psychologist to propose a more adaptated therapy for the patient. Denial must be taken in a dynamic perspective and not as a direct negative consequence of the cerebral injury. In such situation, the priority is not to suppress denial but rather to consider it is the way the subject should face laborious situations imposed by the reality.