The signs and symptoms of dementia are termed as the neuropsychiatric symptoms, also known as the behavioral and psychological symptoms of dementia. Behavioral symptoms can include agitation, restlessness, inappropriate behavior, sexual disinhibition, and aggression, which can be verbal or physical. These symptoms may result from impairments in cognitive inhibition. Psychological symptoms can include depression, hallucinations (most often visual), and delusions, apathy, and anxiety. The most commonly affected areas include memory, visuospatial function affecting perception and orientation, language, attention and problem solving. The rate at which symptoms progress occurs on a continuum over several stages, and they vary across the dementia subtypes. Most types of dementia are slowly progressive with some deterioration of the brain well established before signs of the disorder become apparent. Often there are other conditions present such as high blood pressure, or diabetes, and there can sometimes be as many as four of these comorbidities.

People with dementia are also more likely to have problems with incontinence: they are three times more likely to have urinary and four times more likely to have fecal incontinence compared to people of similar ages.

Dementia symptoms can vary widely from person to person. It affects memory, attention span, communication, reasoning, judgement, problem solving and visual perception, etc. Signs that may point to dementia include getting lost in a familiar neighborhood, using unusual words to refer to familiar objects, forgetting the name of a close family member or friend, forgetting old memories, not being able to complete tasks independently, etc.