急性辐射综合症，也被称为辐射中毒或辐射病（英文缩写ARS），是一种患者在24小时内暴露于大剂量的游离辐射下导致的症候群，症状可持续多达数个月。 本术语意指急性医疗问题，而不是产生于长期辐射暴露的慢性辐射综合症。

发病和症状类型取决于患者的辐射暴露情况。剂量较小的辐射对消化系统产生影响，比如恶心，呕吐，血指数下降的相关症状如感染和出血。大剂量的照射会导致神经系统损伤症状和快速死亡。治疗急性辐射综合症的一般方法为输血和抗生素。

引发慢性辐射综合症的低剂量辐射，虽不能导致急性综合症，但经年累月的照射下也可能出现类似的症状。 辐射暴露同时也会提升某些其他疾病的罹患几率，比如癌症。 这些疾病有时也被作为辐射病来提及，但它们从不被包含在急性辐射综合症中。

Acute radiation syndrome (ARS), also known as radiation poisoning, radiation sickness or radiation toxicity, is a collection of health effects which present within 24 hours of exposure to high amounts of ionizing radiation. The radiation causes cellular degradation due to damage to DNA and other key molecular structures within the cells in various tissues; this destruction, particularly as it affects ability of cells to divide normally, in turn causes the symptoms. The symptoms can begin within one or two hours and may last for several months. The terms refer to acute medical problems rather than ones that develop after a prolonged period.