Alzheimer's disease is the most common form of dementia, and accounts for 55% of all identified cases of dementia. This incurable, degenerative, and terminal disease was named after the German psychiatrist Alois Alzheimer in 1906, after he first described the condition. Generally it is diagnosed in people over 65 years of age, although the less-common early-onset Alzheimer's can occur much earlier.

Although Alzheimer's can affect each individual in many unique ways, there are many common symptoms. In the early stages, the most commonly recognised symptom is memory loss, such as difficulty in remembering recently learned facts. When a doctor or physician has been notified, and Alzheimer's is suspected, the diagnosis is usually confirmed with behavioural assessments and cognitive tests, often followed by a brain scan if available. As the disease advances, symptoms include confusion, irritability and aggression, mood swings, language breakdown, long-term memory loss, and the general withdrawal of the person as their senses decline.

The cause and progression of Alzheimer's disease is not well understood. Research indicates that the disease is associated with amyloid plaques which cause damage to neurones and brain tissue. Currently-used treatments offer symptomatic benefit; although no treatments to delay or halt the progression of the disease are as yet available.

Mental stimulation, exercise, and a balanced diet are often recommended, as both a possible prevention and a sensible way of managing the disease.