Book excerpt: CAMDEX-DS is a comprehensive assessment tool for diagnosing dementia in people with Down's syndrome (a group known to be at particular risk of dementia). Based upon CAMDEX-R, CAMDEX-DS has been modified for use with intellectual disability. In order to differentiate decline due to dementia or other mental disorders from pre-existing impairment, particular emphasis has been placed on establishing change from the individual's best level of functioning. The pack is comprised of a structured informant interview, a direct assessment of the patient/participant (CAMCOG), and guidance for diagnosis and post-diagnosis intervention, providing a reliable way to identify dementia (and to differentiate it from other common disorders). It may be used in community settings by mental health professionals as part of the diagnostic process, or to formalize diagnosis in the context of research. Use of the CAMCOG provides the means for ongoing neuropsychological evaluation and informs future support and intervention strategies.