Alzheimer's disease can last between five and 20 years from the onset of the first symptoms to death, although some patients may go through a period of one to two years when they do not seem to change much. Symptoms are often present for about one to two years before it becomes apparent to family members that the changes are not simply a part of normal aging. Often people who suffer from Alzheimer's disease appear normal to casual observers, although family and close friends are usually aware that something is not quite right. They may appear depressed as they withdraw from an environment that they find increasingly confusing. This constitutes the earliest (or first) phase of the illness.

As the years go by, people with Alzheimer's pass into the long second stage of the illness. During the early part of this phase, they need only minimal assistance, but lots of compassion, understanding, and patience from their family members. As the illness progresses, they begin to need assistance with dressing and bathing. They lose the ability to leave home alone and can no longer safely operate a car or work in the kitchen. Toward the end of this phase, they may forget how to do even the simplest of tasks such as combing their hair or brushing their teeth. Even well-learned information, such as the names of their children or spouse, are erased from their memory. They may feel that their home is not their own or that their spouse is really their parent or an impostor. Eventually, they require assistance to dress, bathe, use the bathroom and eat. They may have considerable difficulty speaking and may be incapable of making even the simplest decision. This second phase can last three to 18 years. It ends at the point when 24-hour care is required.

The third stage covers the period from the onset of total care to death; it usually lasts one to three years. At this stage, most people are in a nursing home. They have usually lost all concepts of past and future; their world is limited to the present. They may not recognize family members though they usually are aware that they are "friendly" people who care for them. They lose all bowel and bladder control and toward the latter part of this stage become lose the ability to walk. Near the end, they lose the ability to speak and to swallow and may refuse to take food or liquid by mouth. Death intervenes at this point.