Insight in dementia is a multifaceted concept and ability, which includes the persons' perception of their behavioral and cognitive symptoms and functional disability. This ability seems to deteriorate as dementia progresses. The aim of this study was to evaluate the level of insight in the cognitive, behavioral, and functional disorders in a group of persons with mild cognitive impairment (MCI) or mild AD (Alzheimer's disease) and to compare their perception of their illness with that of their caregivers. The study involved a group of 121 persons with MCI and mild AD and their caregivers. The persons with MCI and mild AD were administered the tests Mini-Mental State Examination, Instrumental Activities of Daily Living, Activities of Daily Living, Neuropsychiatric Inventory, Schedule for the Assessment of Insight, Clinical Insight Rating Scale, and a short interview. Major differences were identified between how the persons with MCI or mild AD and their caregivers perceived the persons' cognitive and behavioral disorders. The group with MCI or mild AD underestimated their deficits, which were considered serious and disabling by their caregivers.