In most cases, the symptoms of dementia progress gradually, often over a period of several years. The early signs (usually memory problems) are normally subtle and may not be immediately obvious.

The symptoms of dementia can vary greatly, but those with dementia often have one or more of the following:

• Problems with memory - this may include forgetting the names of people they know well, or forgetting where they live. Normally, recent memories are affected first, with memories of events further in the past only affected once the dementia becomes more developed. As dementia progresses, memory loss may affect memories of recent events so completely that the person appears to be living in the past - they may even think of themselves as young and not recognize their true age.
  
• Problems with speech and language - they may forget simple words, may use the wrong words without noticing, or their conversation may become simplified, repetitive or irrelevant.
  
• Confusion - they may become confused in new surroundings or by new people, or about who or where they are. They may lose track of time so that they are unsure what day it is, or even whether it is morning or afternoon.
  
• Changes in mood or behavior - they may become irritable or aggressive. As dementia progresses they may lose their normal inhibitions and begin to say or do inappropriate or antisocial things; in some cases this can include inappropriate sexual behavior. They may lose interest in the outside world or their own care, giving up interests and hobbies, paying little attention to their personal hygiene, or forgetting to wash or change their clothes.
  
• Difficulty performing simple tasks they may have difficulty doing everyday tasks such as cooking a meal. They may begin cooking and then wander away, forgetting what they were doing, or they may prepare a meal and then forget to serve it.
  
• Problems learning new information, ideas or skills.

Some types of dementia can cause less common symptoms, including:

• hallucinations,
• obsessive or repetitive behavior,
• the belief that they have done or experienced things that never happened (confabulation),
• disturbed sleep, or sleeping in the daytime and being awake at night,
• depression,
• physical deterioration, loss of appetite, loss of weight and increased vulnerability to infection, and
• incontinence.

If dementia becomes severe, it can cause other symptoms, including:

• difficulty with swallowing,
• difficulty changing position or moving from place to place without assistance, and
• complete loss of short-term and long-term memory.

Sometimes, those with dementia are unaware that they have any symptoms, especially symptoms that affect behavior.

Many conditions (such as depression) have symptoms similar to dementia, so it is important not to assume that someone has dementia just because they have some of the symptoms above.