The diagnostic criteria for AD requires: 1) evidence of cognitive decline as compared to baseline cognition, and 2) impairment in multiple cognitive domains, including language, motor function, recognition, and planning/organizing. This criteria must be distinguished from any lifelong impairment that the patient may have, and delirium.

The diagnosis of AD may be clouded by several factors, including: age, intelligence, education, cultural background, psychiatric illness, sensory deficits, and comorbid conditions.