Summary 　せん妄は，脱水や感染などの身体要因や薬剤の影響によって引き起こされる一過性の脳機能障害であり，意識の変容や注意力の障害，認知機能障害などを生じる。そのため，患者は自分が置かれた状況を認識することが困難となり，あらゆる面において大きな影響を与え，強い不安や苦痛を生じる。また，患者のみならず家族や医療者にとってもコミュニケーションが困難となり，大きな負担を生じる。 　せん妄は重症化すると回復が遅れ介入効果も減少するといわれており，早期発見・早期介入がケアのポイントとなる。せん妄が起きた場合には，患者との積極的な関わりを通して現実見当識を補強することにより患者の安心感を高め，二次的な問題を回避することが重要である。 Delirium is a transient disorder of brain function that can be caused by various factors, including dehydration, infection, other physical problems, or effects of drugs, and is primarily characterized by alterations in consciousness, attention, and cognition. Because of these abnormalities, patients with delirium have difficulty understanding the situation they are in, which in turn has significant impact on the patients in various ways that make them feel significantly anxious and distressed. Consequently, increased burden is placed not only on patients but also family members and health care providers, because of difficulty in communicating with the patients. For successful care of delirium, early detection and early intervention are critical, because, once it becomes severe, interventions are less effective and recovery requires prolonged time. When delirium is noted, it is important to actively communicate with the patient to improve the patient's orientation and reassurance of reality, in order to avoid secondary problems.