Delirium is defined as non-specific organic brain syndrome in which disturbances of consciousness is associated with attention, perception, memory, psychomotor-activation, mood, and steep-wake cycle disturbances. Despite being the most common mental state disorder, it is overlooked by clinicians. It remains unrecognized in about 70% of old patients. This is due to unawareness rather than misdiagnosis. Neglect is not the only trouble in diagnosing delirium. Physical and psychiatric sign and symptoms of delirium may mimic many other medical and psychiatric diseases. Systemic diseases, central nervous system disorders, toxic effect of drugs or addictives and environmental factors may result in delirium. Risk factors identified in delirium may lead to confusion by interfering with the bottom-up effect of the ascending reticular activating system on attentional matrix. by disturbing the top-down control of attentional matrix executed by frontal, parietal and limbic cortex or by affecting domain-specific attentional modulation. Because of its high morbidity and mortality, delirium prompts urgent treatment and must be recognized by every physician. In this review, to update our knowledge, the causes and risk factors, clinical findings and management options for delirium are summarized.