Adequate diagnostic information can be considered a basic intervention in dementia care. However, clear diagnostic disclosure in dementia is not yet regular practice and the evidence regarding patients' preferences for or against disclosure is scarce. The aim of this study was to give an in-depth description of the impact of receiving the diagnosis of dementia, both on patients and the patients' proxies. The method used was the design of a grounded theory interview study. Analysis of the interviews revealed that disclosure had an impact on three key domains: awareness of dementia, partnership, and social relationships. Most patients and carers reported that they had experienced the disclosure of the diagnosis as a confirmation of their assumptions. A minority of patients and carers felt threatened and shocked by the diagnosis, because they did not expect it. The findings of this analysis challenge current opinions and practice about diagnostic disclosure like obstacles anticipated by clinicians such as inducing negative feelings and causing harm. Disclosure of the diagnosis of dementia can generally be carried out without introducing stress for the patient or carer and facilitates guidance. Therefore regular practice should include the careful planning and performance of diagnostic disclosure.