This article investigates how secrets and lies affect Alzheimer’s disease and other forms of dementia. Based on two singular cases, it analyses different configurations of secrets in their temporal dimension- following their evolution over time- and their relation to social spaces: who is excluded, who is involved, and why? Diagnosis disclosure cannot be resumed by the alternative of telling or not telling. It depends upon the people and the social spaces involved. Secrets appear as a way to manage the stigmatizing consequences of disclosure in terms of self-image, status and also opportunity to carry on the meaningful activities. Different kinds of lies influence relationships with relatives: beyond the diagnosis issue, secrets and lies depend on how the situation itself is defined in terms of dependency or disability. These secrets, and sometimes lies, reflect what matters to people and gives sense to their own lives. They reveal different ways of protecting identity and relationships which form the heart of the personal conduct of Alzheimer's disease patients, friends and families.