急性（Acute）在医学中指发作迅速持续时间可能也较短的病症。有时侯，急性与慢性用来区分不同的病，比如急性白血病和慢性白血病；有时候，急性用来强调发病突然，如急性心肌梗塞。

In medicine, an acute disease is a disease, a short course, or both.

Acute may be used to distinguish a disease from a chronic form, such as acute leukemia and chronic leukemia, or to highlight the sudden onset of a disease, such as acute myocardial infarction. The word "acute" may also be used in the context of medicine to refer to the acute phase of injury, meaning the immediate post-injury healing processes.