Dementia: Significant loss of intellectual abilities, such as memory capacity, that is severe enough to interfere with social or occupational functioning. Criteria for the diagnosis of dementia include impairment of attention, orientation, memory, judgment, language, motor and spatial skills, and function. By definition, dementia is not due to major depression or schizophrenia. Alzheimer's disease is the most common cause of dementia. Other causes include AIDS, alcoholism, brain injury, vascular dementia (damage to the blood vessels leading to the brain), dementia with Lewy bodies, brain tumors, drug toxicity, infection of brain, Creutzfeldt-Jakob disease, meningitis, Pick disease, syphilis, and hypothyroidism.