The term anosognosia refers to the condition in which a person with a disability appears to be unaware that they are suffering from a disability. A person with anosognosia is not in denial; rather, they are actually unaware of the existence of their disability. The term comes from the Greek words for disease (nosos) and knowledge (gnosis), and literally means "to not know a disease." Anosognosia is often associated with a physical brain injury, but it can also occur in disorders like schizophrenia.

It is not uncommon for some people with schizophrenia to have an extreme lack of insight into their mental illness, and the term anosognosia may be used to describe this situation. Schizophrenic anosogosia is also the result of damage to the brain and seems to be particularly associated with damage to the right hemisphere, with the frontal lobe and part of the parietal lobe the parts of the brain most involved. Schizophrenic anosogosia may not be constant--some people have times when they are aware of their illness, particularly when they are in remission, and other times when they lose this awareness.

According to the National Alliance on Mental Illness, anosognosia is the single largest reason why people who suffer from schizophrenia and bipolar disorder do not take their medications as directed. Because they don't recognize that they're suffering from a mental illness, people with anosognosia see no reason to comply with medication instructions. It can be frustrating for caregivers and loved ones, and can lead to the worsening of symptoms. Many schizophrenics--approximately one-third, according to studies--see improvement in their anosognosia when they take antipsychotic medication.