This document summarizes organic mental disorders, including delirium and dementia. Delirium is characterized by a disturbance in consciousness and cognition that develops rapidly over hours or days, with reduced attention and disorganized thinking. Dementia causes a global impairment of intellect, memory and personality without impaired consciousness, and is usually progressive and irreversible. The disorders discussed are due to demonstrable brain disease or dysfunction from systemic illness, and can result from various medical conditions, medications, toxins, or significant neuronal loss in brain regions involved in memory and cognition.