While dementias represent an important problem of social health, they remained underdiagnosed. Data from the literature suggests that only 30% of cognitive impairment are detected and correctly evaluated, while most of the patient (up to 90%) and caregivers (up to 70-80%) ask for a precise diagnosis. Proper evaluation increase diagnostic accuracy from 30% to 80% but 20% of diagnoses remains inexact. Diagnostic disclosure seems to have a positive impact on patient's affective symptoms but is associated to an increase of suicide during the following 3 months, and thus must be a progressive and controlled process. Accompanying a patient in this process necessitates complexes competencies from the primary care physician. Difficulties related to this disclosure are counterbalanced by benefits for both patient and families.